Tor is an anonymity and censorship circumvention network. Due to abuse by vandals, Tor exit nodes are usually blocked from editing Wikipedia. Tor users who wish to edit Wikipedia have to request IP block exemption. No restrictions are placed on reading Wikipedia through Tor.
Tor users should be met with good faith, as there are good reasons to use anonymity networks. In countries that censor Wikipedia or block it completely, it is one of the few ways of accessing Wikipedia. Additionally, in light of governmental surveillance programs, users may choose to use Tor in order to exercise their right to anonymity.
The policy on open proxies allows open proxies to be blocked from editing at any time for any duration. Currently, the MediaWiki software's TorBlock extension automatically blocks all editing through Tor except where an account has been granted IP block exemption. Because Tor is often abused by vandals, users of the English language Wikipedia will often find that Tor exit nodes have been completely blocked, prohibiting account creation and editing by registered users (without block exemption).
Registered users in good standing can ask for IP block exemption to be enabled on their accounts. The exemption allows logged-in users to edit from IP addresses that are nominally blocked. IP block exemption should be requested by sending a request to the Unblock Ticket Request System. However, it may be difficult to establish good standing and remain completely anonymous, as the former requires editing without using Tor.
A group of Wikipedia editors have set up several closed proxy servers that can be used by editors normally blocked from editing by the Chinese firewall. Users who wish to use one of these proxies to edit can find more information at the WikiProject on closed proxies.
Tor, one of the most famous anonymity browsers, is the only anonymity network which is systematically blocked on Wikipedia. Other anonymising proxies are likely to be blocked, but many are not. Some may be only soft-blocked, allowing an account to be established.
Wikipedia:IP block exemption#Used for anonymous proxy editing describes how to make a request to the UTRS system to have an account created with a permission to circumvent Tor blocks (account creation and the ordinary request process are blocked from Tor proxies due to vandalism issues). You should immediately change the password after logging in.