To download
You don't need to have an account to download skip files. Just search or browse for the title and download the file on the video's page. Some movies have more than one file available because users are encouraged to improve them for everyone's benefit. Newer, presumably more polished files will appear at the top. The description on the video page will indicate what content the file will skip but you can click on the skip file for more details as provided by the author.
To upload
You do need to have an account for this.
Simply search for the video that you are interested in.
For certain common titles, there may be many matches so make sure you choose the year that correctly corresponds to the version for which you have created the skip file. If a skip file already exists for this video in question, you can use that as a starting point or create yours entirely from scratch.
Note: this website is only for exchanging skip files. Posting any other material will get you banned permanently after the first offense.
To request
You will also need to have an account for this.
Simply search for the video that you are interested in.
For certain common titles, there may be many matches so make sure you choose the year that correctly corresponds to the version you are requesting. If a request already exists for the video, you can simply up-vote that request but if you are looking for a skipfile that filters different content than the existing request (different categories or different levels) you will need to create a new request.