Contacts, broadcasts, segments and getting your sending set up.
A tag is a label you put on people so you can find them again. Tags live in Subscribers, under Contacts, in the Groups panel.
One email to your whole list, sent now or later. Nothing sends until the last of four steps.
Upload the file you already have — CSV or Excel. No tidying first: it reads your headings and shows what it decided before anything is saved.