On the Markets page you can view all the available collateral types.
The page shows the current borrow rate, total amount of $crvUSD borrowed, and total amount of collateral backing it.
If you do not have a position, you can click on any market to create a loan.
If you already have a position it will show a dollar sign overlay on the left, and clicking on the market will take you to a page to manage your loan.

Collateral Choices

While testing $crvUSD, the team created a market for $sfrxETH with a small market cap ($10MM) because it had a compatible oracle. Additional forms of collateral are expected to be approved by the DAO.