I truly cannot find this information on my brokerage website.

I have a brokerage account for my HSA, and if I wanted to use this same brokerage to invest cash I have sitting in my bank acct. would I:

 1. transfer into this previously-created account that I linked to my HSA custodian
 2. create a new "Individual" account?

I'm assuming the 2nd (from colloquial knowledge and common sense), but I'm confused why my brokerage would offer the option to "transfer cash from a bank account" to my HSA-linked account.

I use TDAmeritrade.