Intermission: Devoicing
Intermissions are optional.
In certain places, the vowels "u" and "i" can be "devoiced", meaning that they're not pronounced at all. です and でした are examples. It's still acceptable to pronounce the vowels in these cases, but you'll sound weird.
| Desu | De-s |
| Deshita | De-sh-ta |
Don't bother learning any more about devoicing until you're much better at japanese. It'll make it harder to notice irregular devoicing patterns that people don't bother teaching.