When delegating to a dRep (or self) you only delegate the voting power that you were assigned due to Ada you hold. YOU NEVER DELEGATE YOUR ADA!
Your Ada always stays in your wallet and it’s always available for you to use regardless of which method you use to delegate.
If you become a “direct voter”, you basically register as your own dRep. That will require a 500 ADA deposit (that you get back when retiring). You can delegate your other wallets/accounts to that dRep ID and could even advertise to get delegations from other people.
The only difference is that gov.tools doesn’t ask you to give metadata for the public lists of dReps.
They invented the term “direct voter” for that because they thought it is more user-friendly. Cardano itself doesn’t know that distinction. They are all just dReps if advertising for delegations from others or not.
You probably need the dRep ID of the dRep you want to delegate to.
Lists of dReps can, for example, be found on https://gov.tools/drep_directory or https://tempo.vote/dreps. And people who are dReps and whom you might trust with your delegation typically also publish their dRep IDs somewhere on their profiles or websites.