If you are growing tomatoes from seed they need to get going early February in time to plant in Houston.
You want to spend about 6 weeks growing them indoors before placing them outside. Find a very sunny window to get them going and remember tomatoes love heat so be sure your location is very warm as well.
It is unlikely you’ll need to add heat down here in Houston, but up north heating pads on their lowest setting are sometimes put under the trays of tomato seeds or the seeds can be placed on a radiator in the evenings.
Mid-March is when tomato plants typically go in the ground outside here. You need night temperatures over 50’F to safely plant them outdoors. If it gets chilly after you’ve put them out cover them with milk jugs or plastic to protect them.
Tomatoes have two very short growing seasons in Houston, one in the spring, one in the fall. You need to be sure to get in early on both if you want tomatoes. If it is too chilly, cover them with plastic. One the night temperatures bottom out around 70’F the plant will stop making flowers.
I usually collect seeds from heirloom tomatoes purchased at the market. Just stash a few seeds when you slice the tomatoes. Place them on a paper towel to dry out. Once they dry out you can pot them.