People often ask how many platforms they need, as if there were a set list to work through. There is not. New advertising channels appear every year, and the ones you have heard of (Google Ads, Meta, TikTok, and the rest) are separate products with separate logins, built by different companies to solve different problems. Sharing the "Google" name does not mean two of them talk to each other, and there is no prize for using all of them.
The useful way to think about it is by role: the job a platform does in your marketing. There are only a handful of roles, and most businesses need two to four platforms in total. Once you can name the roles, you can tell which platforms earn their place, and in what order to add them.