Stake SEXP to mint sUSD. The other synths can be obtained by trading sUSD for them in the Synth Swap. Your C-ratio is a ratio of the value of your locked collateral and your share of debt. When minting, you need 4 times as much collateral value as the value of the sUSD that will be minted -- the C-ratio will be 400%. Make sure to maintain your C-ratio at or above 400% to claim fees. This is automated by keeper bots, so you don't have to claim manually. If your C-ratio drops to 200% or less, you will be marked for liquidation. You have 3 days to bring your ratio back to 400% to avoid liquidation. You can increase the C-ratio by adding more collateral or burning sUSD.
When your ratio is below 400%, you also have the option to self-liquidate some of your collateral. This will bring your ratio to 400% automatically at the cost of an additional 10% penalty compared to just burning sUSD or adding collateral. In case you are marked for liquidation, the self-liquidation will also remove the liquidation mark and the associated deadline above.