In order to finish this type of tasks, you need to be a member of a forum, in most cases for different tasks, even member of several forums. Registrations for forums is easy, some forums require e-mail confirmation, and some don't. Every forum has their own general rules, and it is always advised to read all of them in order to make successful posts and those posts are not considered as spam by the administrators/moderators of the forums and deleted.
Almost every forum task in Microworkers requires a new post in the forum. What you need to do is chose the active forum or subforum from the forum you are a member of, which is related to the topic given from the employer, and open a new topic. You should give a title to your topic (post) in the subject line. Forums do not allow websites links in the title of the post, so make sure the title is related to the topic your post will be about. Next, post the body of the post, write meaningful content which will capture the attention of the forum readers and will be useful so readers/visitors will be interested to actually visit the provided link in the post.
Employers in the task instructions give url and anchor text. An example of it may be this:
URL to link to: http://www.thextremelimos.com/
Keyword / Anchor text: party bus los angeles
use a simple code which is shown in this image
After you finish writing your post, click on submit, and submit the url of the forum post as proof. Some employers also ask for your forum username as proof.
I think I have explained the basic points for these tasks, any comment is welcome and valuable