The Welcome Category is a section to read Community News, Rules, and to Read/Post User Introductions. If you want to write an intro, please use the New User Introductions category. You may mention what you sell, but if you want to make an advertisement, that should go in My Fiverr Gigs.
Fiverr Tips is a section to read Community News, Rules, and to Read/Post User Introductions. Please post tips in individual categories. Tips for Sellers and Tips for Buyers is for original tips posts to sellers/buyers. If you are asking for tips for yourself, do that in Improve my Gig.
Fiverr Experience has subcategories for users to tell their stories, have general discussions and otherwise share about their experience. Please post in the appropriate subcategory if you want to post about your experience.
The Fiverr Site Category is a section for information about the entire Fiverr website. There are categories within this section to report bugs to the community, make suggestions about the fiverr.com site, etc.
The Events category is primarily for staff and moderator use and contains links to the official Fiverr podcasts, live events, community events, etc. There are subcategories where comments are welcome, but in general events should be cleared with Fiverr before being announced in this category.