I made just a little jar of salsa the other day. It's pretty easy. You can tailor the portions to your exact likings, but this is what I used
2 tomatoes (I used vine), diced
1/2 yellow onion, diced
1/4 cup chopped cilantro
1 clove garlic, minced
salt and pepper to taste
1-2 tsp cumin
juice from 1/2 a lime
That's the base, then the peppers depend on the spice factor. Mine was RIDICULOUSLY spicy. I thought it was too spicy, but my husband has a high spice tolerance and he thought it was perfect. I used 1 serrano, 1 red chili, and 1 habanero (I know...spicy) lol. I suggest you start with about 1/4 or 1/2 of each and add more to get it to the spicyness you desire.
That made about 1 jar of salsa...just enough to last a few days and stay fresh. A lot of the salsa recipes I see use 8-10 tomatoes and that just makes way too much salsa for me to possibly eat before it goes bad. I like mine uber fresh.
I also don't use a blender. You could always blend it to get more of a crushed salsa like you would get at the store, but I'm more of a pico de gallo person, so I prefer it chunky and raw. The lime juice and the tomatoes make a little bit of juice after a few hours, so its a nice balance between fresh, chopped ingredients, and some liquid (without having to add water).
Salsa can really be experimented with. Salsa Verde uses tomatillos as the base, salsa cruda is uncooked (vs cooked), pico de gallo refers to raw, chopped sauces. Most salsa people think of are salsa fresca and although pico de gallo can be called salsa fresca, salsa fresca can also be pureed (thus making it not really pico de gallo style)