Welcome! And sympathy for losing your Mom.
I would suggest starting with easy plants, which in my mind means annuals. Zinnias and marigolds are easy, even if you start them from seed.
After a year or two, you're bound to see plants you like the looks of, and then is soon enough to try more difficult things, like starting perennials from seeds.
If you can spend money on buying plants instead of starting from seed, you can just go to a few big box stores and walk around the garden section, picking out what looks good and isn't too expensive.
A few healthy, small, cheap plants in tiny pots are MUCH better than one big, expensive plant that outgrew its pot a month before you bought it. Once you put it into soil, it will grow and be healthier than a big, root-bound plant trying to recover from Wal-Mart's abuse.
IF you find a clerk that seems to know anything, asking which are easy to grow in YOUR climate would be smart ... but big box stores tend to sell anything that they can move, whether or not it is well suited to the local climate!
I heard you say "CA", and "sunny". You might need to focus on resistance to heat and dryness.
1.
It might be smart to do as much soil preparation as possible BEFORE bringing plants home, or starting seeds. If its easy to drop them right into the soil as soon as you get them home, you will. If you aren't ready, you might do what I do and the plants could well die in their tiny pots before you get around to planting them out.
2.
Pick the spot: sunny and near enough to a faucet that you can water easily.
Somewhere you like to sit and gaze. Somewhere you'll walk past often.
Somewhere you can see from a window?
3.
If you have awful, awful soil, it MIGHT be easier to grow in pots than in the ground, but growing in pots has its own set of challenges. Real living soil in contact with the entire Earth is much easier to keep healthy and congenial for plant's roots than a soulless mix in a plastic pot.
Dig up the soil a little where you plan to grow. Loosen the soil and break up clods. Pull weeds, and add compost even if you have to buy a few bags.
4.
Don't over-fertilize! That's easy to do with chemical fertilizers, can easily damage or kill plants, and may be difficult to recover from. . Under-fertilizing hardly hurts plants at all, at worst it slows their growth. One rule of thumb is to fertilize "weakly, weekly", at least in pots.
When you grow in the ground, you can feed the soil with compost. Then the soil feeds the plants without danger of over-fertilizing.
5.
Buy or collect some bags of mulch (like bark or wood chips or pine needles or brown leaves) before you buy plants. If you throw down mulch right after weeding, few new weeds will sprout (they need to see the sun before they come out of dormancy. You can weed, and weed, and weed, and weed, and then put down mulch ... or you can weed once, put down mulch, and then just pull a few weeds, occasionally.
When you're ready to plant, weed again, push mulch away from where you want the plant, dig the hole, plant the plant, smooth & water the soil, then cover as much of the soil as possible back up with mulch.
Mulch keeps rain from compacting the soil surface. It keeps the sun off the soil surface, which keeps soil moist longer and much cooler. It "smothers" weeds (actually mulch keeps them from germinating)
6.
Only grow things you like! Look at a photo or a bloom in the store. If you don't go "AHHHH!", why bother?
Until you get a "system" down pat, you'll be expending time and effort and thought, so never buy or plant something that someone else thinks you should grow. You should like the way it looks, or it should remind you of your Mom, or at least the name should sound cute to you.
