If you have a DNAGedcom Account and did not link it during signup, head over to the Options page to link them. You can see at the bottom if they are properly linked.
The first thing you will want to do is download the Chrome Extension
Check out the Getting Started page for the Chrome extension for info on how to log in, gather matches, and begin tagging.
You can use the website to view and manipulate your data gathered from the various websites.
If you have gathered multiple Kits for the same Person, head on over to the People section and use Merging to combine them into one person.
You can also view your matches over at the Autosomal section.
If you gathered from a site that supports Chromosome matching information, such as MyHeritage, FTDNA, or Genesis, keep an eye out on your match list for the Chromosome Browser icons.