I know I should use the plump helmets for brewing. But what should I use to make them meals with? what should I get them to eat?
And to brew something I have to have "brew a drink" set to a repeated task in the still right?
also with meals in the kitchen?
First let me say that if you actually figure this game out without using a tutorial, you are way more dwarfy than the rest of us.
Now to your question: what to cook?
You can cook plump helmets if you want. Other plants like cave wheat, sweet pods, quarry bushes need to be processed or milled before they're edible, and some (pig tails, dimple cups) are totally inedible. So stick to plump helmets or above-ground berry crops until you figure out the agricultural supply chain.
Typically, most of my cooking is based on meat. At the rate my forts grow, there's always a surplus of meat. This begins when I slaughter the two pack animals that pulled my wagon. Then each batch of migrants will bring a few more useless animals. And my cats and dogs will reproduce like mad. Within the first year I tend to have a good supply of wild meat, too, both as a result of training my military on wild animals and as a result of building bridges over the rivers and putting cage traps on the bridges. Build a butcher shop, and a tanner shop next to it to tan the hides before they rot. Hit (z) then (enter) to get to your animals interface. Choose the pack animals and order them (b)utchered. The butchery and tanning will happen automatically. Make sure you have a refuse stockpile outside the fort so that the dwarfs can dispose of waste material before it rots.
Yes, you can go to the kitchen and queue up "Cook Easy Meal" jobs on repeat. Easy meals take 2 ingredients, Fine meals take 3, Lavish meals take 4.
Soon you may want to appoint a manager to make it easier to queue up work. Make a table and chair, then (b)uild them in a corner or small room somewhere. With (q) move the cursor to the chair, make it a "throne room or study", and assign the chair to someone without a lot of responsibility. Then type (n) for your "nobles/administrators" display. Give that dwarf the job of "manager". Back to the main interface, you can see the manager's queue by hitting (u) and (m). Then (q) to order new jobs, type part of the order, e.g. "meal" and select the order and the number of times you want it done. If you have the manager queue up 30 "cook easy meal" jobs, he'll go find the kitchen and make sure it happens. Unlike when you order it yourself, the manager's jobs won't be cancelled and forgotten if there's no ingredients. He'll keep on trying until the cook makes something.
(By the way, you may also want to give that dwarf the job of "bookkeeper". It's very time consuming so this should be somebody without other important jobs. After making him bookkeeper, hit (s) for settings and set his counts to "most accurate". This will allow you to see exactly what you have in your stockpiles at all times.)