Unless you're using a 'Guest' account on someone else's Chromebook, you'll need a
Google account. With a non-Gmail email address, you can create a Google account. Once set up, you'll be immediately signed into Google services on your Chromebook, and you can sync your bookmarks, extensions, preferences, and passwords between browsers if you use Chrome on another system.
Mostly web-based programmes, dubbed 'Apps' by Google, but also Extensions, which attach to the browser and enable for interaction and notifications. Apps use the same programming language as web pages, but they're tailored to the Chrome experience.