How do I combine text from several cells into one cell?

CONCATENATE (or the shorter & operator, which does the same thing and is easier to read) joins values with no separator unless you insert one manually between each pair, like =A2&", "&B2&", "&C2. That gets repetitive past a few cells.

TEXTJOIN solves that: give it a separator once, tell it whether to skip empty cells (TRUE is usually what you want), then list a whole range. =TEXTJOIN(", ",TRUE,A2:C2) joins every non-blank cell in A2:C2 with a comma and space between each, without repeating the separator manually for every cell.