Onions I found easier to start from sets than seed. So I just buy a bag of sets each year.
Garlic, you just plant the cloves in the late fall and cover them with some hay or leaves or something (in case it's too cold), and they'll poke up first thing in the spring.
Do you know what your growing zone is where you are?
If you want to grow stuff that's more sensitive than your growing zone, you'll want to look at a greenshouse, but for smaller spaces, this little hoop house works great!
I built one of these and actually put it inside my greenhouse, so I can start growing heat loving plants like watermelon, basil, and peppers starting in February.