Growing lettuce in the Sacramento valley is a bit different than growing it in other places. This is because lettuce does not like heat. The average American salad consists of lettuce and tomatoes - but surprise! these vegetables do not happily co-exist in our desert/Mediterranean climate (or perhaps anywhere), so once my salads go from spring to summer, they stop containing lettuce and start containing tomatoes. Rule of thumb - tomatoes like it hot; lettuce doesn't.
Lettuce is easy to grow, even from seed. Either buy little seedlings, start seeds in small pots or seedling containers, or direct sow in the garden. I usually do just those first two - I haven't had luck direct-seeding in the garden. If you plant a leafy variety, you can keep harvesting the outer leaves and let the inner ones replace them. At some point, if you have a lot of lettuce, you'll have more than you can eat, and if the weather warms up, or you can't harvest them in a timely manner, you get what my husband calls "lettuce trees". The taste of these trees isn't as nice, and the texture is a bit tougher, but I eat them anyway.
This year, I've grown both red and green lettuce from seedlings, and I have some green lettuce seeds starting right now, even though it's already getting warm. I specifically chose a heat-resistant variety, but I don't know if that will save them. That's a good idea in hot-summer climates, though - choose your varieties to try to withstand the heat. Lettuce does grow fairly quickly, too, so even if you think it might be too close to summer to plant it, you never really know!