Here's how it works.
You create an account on vanguard. You pick that you want that account to do mutual funds, no brokerage. You choose VTSMX/VTSAX (3k for vtsmx, 10k for vtsax). You supply bank information. Make sure to select e-paper statements to save $20/year. You're done for now.
One or two days later, vanguard makes two very small deposits (10 cents, 20 cents). You go to their website and fill in the details of how much they deposited. This confirms the account is yours and real. They then withdraw those two small deposits within a day, and within a day or two they also withdraw the amount you decided to use for an initial deposit.
You have no fees for having an account as long as you use e-paper statements OR you have over 10k in the account, I believe.
Next, you basically do nothing. The money follows the market decently well.
If you want to deposit more - you just deposit more. The process is simple as long as you're not changing bank details; it just debits $ from your bank account and credits to your fund choice(s).
If you want to withdraw, sure, also easy. If you want to roll dollars from one fund to another, also easy. And so on and so on...
If you want a different type of account (eg, IRA) you just "make a new account" which is a bit confusing, since it links to your main login profile but is indeed a different account. Your web account sees all your holdings / accounts. A tad confusing but that's really the only confusing part.