Um everything
I get research. Can you explain raids if you don't have friends
I've put pokemon on gyms and made them happier with those berry things. That's a bit odd.
Can I ask - you're adults and do you feel a bit ridiculous doing this when the people who are also playing are teenagers? Or is that just me?
Raids.
You can do level 1 raids by yourself, level 2 probably but check you have the right counters, level 3 maybe if you have a good team of the best counters you can do some of them. Level 4 and 5 always need more than one player.
Pokemon Go Type Chart - Poke Assistant
has type charts so you can see what is super effective against what. Weather also makes a difference but not as much as if something is super effective attack.
this is an infographic for the current raid boss selection
The recommended selection prioritises strong defense but raids are totally an attacking thing so you can't rely on recommended and you need to learn the types that are super effective if you want to win level 3 raids on your own, you probably need to be higher level as well to have enough of the right counters at a high enough level, but for instance you might be able to go out and catch 6 weather boosted eevees at level 34 and evolve them all into espeons and that team should be able to beat a machamp... but you probably don't have that team right now
If you live in a town or city you'll probably find that there is a discord, facebook or whatsapp group where people arrange to meet for raids together. If you're in London or a big city there'll probably be one for your local area as well. Depending on how active your area is you can try turning up at level 5 raids at the hatch time and see if a group appears but that can be very hit and miss (Birmingham city centre on lunch hours you can be pretty sure that there'll be groups at most level 5 raids, but outside of those hours you need to be on the discord to reliably find raids, in my suburb it's a facebook group and you really need to be connected to reliably meet for raids).
weather boosting is where you see the swirls around a pokemon on the map, you get +25% stardust and the pokemon is 5 levels higher than normal so you can catch pokemon 5 levels above your current level, up to level 35.
Gyms
6 pokemon per gym, only one of a species can be placed so there's more variety.
When you place them they have just below their actual CP and over time this degrades. When you attack a gym, a pokemon with a full heart will take 3 battles to remove from the gym, this drops to 2 and then 1 over time as the motivation decreases.
You get coins when your pokemon gets kicked out of the gym, maximum 50 per day. Coins are accumulated at the rate of 1 per 10 minutes defended, so you need just over 8 hours total to get all your coins each day.
With research, you get a legendary after doing 7 days of research, and they change each month so you have just enough time to get an articuno before it goes away and something else comes in July if you do one task per day now to the end of the month.
I play in two areas - mostly on my lunchbreak in birmingham city centre with hardcore raiders who are mostly 25-40 year old white men (basically my demographic but I'd prefer something more mixed) and on weekends/community days with a group in my local area which is more mixed but still mostly adults and some parents with children, not teenagers. I feel a bit ridiculous playing it full stop, but I don't really care as it gets me out walking and fulfills my collecting urge for zero cost.