Don't be afraid of making the odd mistake, there are any number of others eagerly waiting for a chance to correct it!
OK that's the official welcome over with. There has been some discussion in the past about if we should have "how to" type pages on wikipedia. The decision is not finalised but I personally have stopped adding material to the experiments page here preferring to use (our sister project) wikibooks instead. See Wikibooks main page for details theresa knott 14:24, 6 May 2004 (UTC)
The developer team at Wikimedia is making some changes to how accounts work, as part of our on-going efforts to provide new and better tools for our users like cross-wiki notifications. These changes will mean you have the same account name everywhere. This will let us give you new features that will help you edit and discuss better, and allow more flexible user permissions for tools. One of the side-effects of this is that user accounts will now have to be unique across all 900 Wikimedia wikis. See the announcement for more information.
Unfortunately, your account clashes with another account also called Oliver12. To make sure that both of you can use all Wikimedia projects in future, we have reserved the name Oliver12~enwiki that only you will have. If you like it, you don't have to do anything. If you do not like it, you can pick out a different name. If you think you might own all of the accounts with this name and this message is in error, please visit Special:MergeAccount to check and attach all of your accounts to prevent them from being renamed.
Your account will still work as before, and you will be credited for all your edits made so far, but you will have to use the new account name when you log in.