@EeveeTinnOk, first welcome to the Sims 4!
Let me start with plants. Wild plants are just one way you get the seeds to plant in your garden. They grow in the different worlds. The key is that you have to be there at a certain time to get the fruit. Throughout the game, all the plants first have to grow before they bear fruit. So when you start a new game, most plants are just a pile of dirt. It takes several days for all the plants in a zone to grow. Some are faster than others. Trees take the longest. Once they grow to full size, then they will bear fruit every day. But you have to be in a zone before 5 AM for the plants in that zone to bear fruit. The fruit starts showing at 5 AM and it takes until 5:30 AM before they bear the maximum number every day. It is the same in every world and zone. Practically speaking, to get all the plants to grow, you have to live in the zone at first to get things going. Visiting other zones and spending time in them helps the plants to grow in those locations. But you have to have an active sim in the zone at the right time for any of them to bear fruit you can harvest.
Seasons introduced seasonal plants. So that adds another factor because most plants only grow in certain seasons so not only do you have to be at the right time of day, but the plants have to be in season. At the end of a season, all the plants that are no longer in season will drop back to a pile of dirt and won't grow again until their season returns.
Seasons also introduced seed packets that you can buy from the computer. There are a couple of different options depending on what packs you have. That is the easiest way to get most of the plants. I'm not sure if you can buy them that way if you don't have Seasons though. I'm not sure if buying the seeds was added to base game or not. If you have City Living, there is also a produce vendor you can buy fruit from but you can't get them all. Vampires, Realm of Magic, Get To Work, Jungle Adventures, and Island Living all introduced different plants to the game.
Once you have a fruit, then you can plant it in the ground or in a planter. Covering your plants by a roof will let them bear all year round. I put most of my gardens on a basement level for that reason.
On controlling sims, what you describe is normal game behavior. Only sims that are in the active household can be controlled. If you send a sim off to work or class, they will go and not be controllable until they return. If you travel with a sim, then the other sims in the household left behind are no longer controllable. The only thing you can do with them is assign them skills to work on, socialize with other sims or care for themselves. Things also depend on where you are. For university, if you are living on campus, you can switch to other sims when a sim heads to class but on a residential lot not on campus, if you follow a sim to class then switch to another sim, it doesn't work. The key thing is if you traveled via a travel screen. If you didn't get a screen then all but the sim you sent away are controllable. If you got a travel screen, then only the sim that traveled is controllable.
Hope this helps you.
