Profiles are a feature designed to allow multiple people to study with Anki on the same device. They may also be useful for testing and other similar purposes, but this is not their primary purpose. Profiles are not recommended for dividing up your content, as doing so is unnecessary and limits your options in terms of viewing statistics and moving content around. Profiles are also unsupported on AnkiDroid.
Anki is designed so that each profile syncs with a single AnkiWeb account – this way, each user can have their own account and use it on whichever devices they want.
If you have created multiple profiles for yourself, the best option is to merge them into a single profile. You can do so by exporting one deck from profile A, and then importing it into profile B, repeating for any other decks in profile A, until everything is in profile B.
If you have different users on your computer, each user will need to set up a separate AnkiWeb account for their profile. Attempting to sync different profiles with the same AnkiWeb account will result in lost data.