Blocking users is very simple.
Visit Special:Block and follow these steps:
IP address, username or block ID: Enter the username, IP address, or IP range to block in the "User" field. Instead of typing this information in manually, it is also possible to click on a "block" link in recent changes, contributions pages, or history pages, which will automatically fill in this field with the appropriate username or IP address. A "Block this user" link is also present in the toolbox when viewing User and User talk pages.
Block type Allows a block to be configured to prohibit specific actions, therefore allowing all others.
⧼block-prevent-edit⧽ If checked, the target of the block will be prohibited from making changes to wiki pages, including editing, renaming, reviewing pending changes, and other change actions.
Sitewide Prohibits the block target from making changes to all pages on the entire wiki and creating new pages.
Partial Prohibits the block target from making changes only to the specified pages and/or all pages in namespaces. All other pages can still be edited, new pages can be created, and files can be uploaded. Up to 10 pages can be added to the block, but non-existent ("redlink") pages cannot be blocked. The corresponding talk and subpages are not automatically blocked and must be entered separately.
Account creation: Selecting this option will prevent the blocked username or IP address from creating new accounts.
Sending email: When this option is selected, the user will be unable to use the Special:EmailUser interface. If an IP address or range is blocked with this option, and it is not set for anonymous users only, accounts logged in from that IP address or range are unable to use Special:EmailUser.
Editing their own talk page: This option is only available if $wgBlockAllowsUTEdit is set to true; it is not by default in MediaWiki 1.25 or lower. In 1.26 or later it is set to true. For a sitewide block, selecting this option prevents the IP address, range, or user from editing their own user talk page. This option is usually ignored for partial blocks; to prevent a partially blocked user from editing their own talk page, the talk page must be specified as a page to block. The only exception to this is where a partial block prohibits the target from editing the "User talk" namespace; in this situation, this option behaves as it would for a sitewide block.
Expiration: Select when the block should expire from the drop-down, or manually type in an expiration time of the block or use the Datetime calendar to select. When manually typing in a time, follow the GNU standard format (eg: 2017-01-01 00:00). The default options in the drop-down may be modified at MediaWiki:Ipboptions.
Reason: The reason selected from the drop-down combined with the other/additional reason specified will be used as the message displayed to the blocked user when they try to edit. The default reasons in the drop-down may be modified at MediaWiki:Ipbreason-dropdown.
Select additional block options (optional): Depending on if a username or IP is being blocked and other options that may have been enabled, some or all of these options will be displayed on the form. Please see Manual:Block and unblock#Configuration settings related to blocking for information of how to enable or disable some of the following options.
Automatically block the last IP address used by this user, and any subsequent IP addresses they try to edit from, for a period of $1: This option is only available when blocking a username. But this is available for both partial and sitewide blocks. When selected, the user's IP will become "autoblocked" (these show up as numbers such as #17 on the active block list) for a short period of time and any other IP addresses that the blocked user tries to edit from will be blocked as well. The duration of an "autoblock" can be changed by adjusting the value of $wgAutoblockExpiry.
Hide username from edits and lists: When selected, the blocked username will not be added to the block log, the active block list, or the user list (only available on sitewide indefinite blocks). Other users with the ability to view these hidden entries will still be able to see and unblock the username or IP address. This option is not enabled in a default installation of MediaWiki; the person putting the block in place must have the hideuser permission. See Manual:User rights.
Watch this user's user and talk pages: When selected, this adds the blocked user's user page and user talk page to your watchlist.
Apply block to logged-in users from this IP address: This option is only available when blocking an IP address. When selected, registered users who try to edit using a blocked IP address will still be able to edit. Otherwise, they will be unable to edit as well.
Double-check everything you entered and click on Block this user. A message should appear saying if the block was successful or unsuccessful.
Unblocking
To unblock a username or IP address, go to the active block list and click on the Remove this block link next to the user or IP you wish to unblock.
Then, enter an optional reason and click on the unblock button.
A message should appear saying if the unblock was successful or unsuccessful.
Alternatively, navigating to Special:Unblock and provide the username or IP.
What it means to be blocked
Sitewide blocked users are unable to edit pages, upload files, move pages, and perform other actions that additional user rights would grant.
Effectively, this makes the wiki read only for those users.
Until MediaWiki 1.17, sysops or others with access to the unblocking interface may still unblock others (as well as themselves if they have the unblockself right).
However, since MediaWiki 1.17, blocked users who are in user groups that allow them to block nevertheless may not block or unblock other users while blocked.
Partially blocked users are only prohibited from performing change actions to the specific pages or all pages inside the namespaces configured.
Known bugs
On the list of active users, the "blocked" status would display for all users who have been blocked at least once after 2017, due to a known bug.
