Just be the way:

You can find another forum user by clicking on the word "Search & Navigation" at the very top menu bar (the white text on black). This gives you a drop down menu with several options. Select the option of "Find user". Click on that and you get to the user list page. There you can search for a user by entering his her her name. (note you can only access this user list page if you have logged in first)

Careful: The search tool in the user list is not fool proof - I have had cases where I couldn't find someone, e.g. because their name was spelled differently than I expected (some people also don't use their real name when setting up their name in the profile; or they may use special characters like ö, ä, é, è which are then difficult for people to reproduce without a German or French keyboard...). So if you don't find someone, another option could be to use the "Advanced Search" (in the same drop down list) and search for their name in the posts that they have made.

Once you have found a user, you can click on their profile (if you are logged in), and then see the last 20 posts that they have made. This is also useful sometimes.

Regards,
Elisabeth