step 1: put the cold milk in together with the starter. turn on the machine and get yoghurt 12 hours later.
step 2: let it cool down to room temperature.
step 3: put in fridge to cool down further. (i prefer yoghurt cold)
as a starter i use any yoghurt from the store.
different yoghurt starters yield different results.
once it's done i freeze a few spoons full of it for the next batches. an icecube tray or a home popsicle maker works well for that.
i keep several generations frozen so when one generation doesn't work out (i don't like the resulting texture) then i can go back to a previous generation.
Vinegar, lemon juice, etc. didn't work to get the smell out of the O-ring, so I ended up just buying another, which I use exclusively when making yogurt. Alternatively, you might be able to just take the O-ring off when making yogurt, since you don't actually need it to be sealed, but I haven't tried this.