If you dont have a reservation for a tent you will have to queue to get in, waiting times depend on the time of day but an hour wait or longer is not uncommon. If you want to get in a tent a see one without a queue or with a small queue I would just reccommend to go for it regardless of which one it is.
All tents have beer gardens which are easier to get a seat in but the real Oktoberfest experience and the real party is in the tent. Nevertheless you can have good time at Oktoberfest just in the beergardens.
The waiters and waitresses work on comission and are paid according to how many beers and meals they sell and they will expect you to order another drink or leave pretty soon after you've finished your drink. A tip is also expected and they wont take kindly to you handing over the exact amount of money. Hanging around to tale in the atmosphere with an empty glass isnt really appreciated because there are hundereds of people waiting outised to take your place who the staff can make more money from. Tables are communal and you will have to share a table with strangers. Obviously finidng space for 2 or 3 is easier than a for a larger group. If you see a few free spaces at a table ask the ocupants if you can join and as long as the spaces are genuinely free they will usually let you.
Hofbräu is the most famous tent, Shottenhammel the oldest. Spaten is is usually the cheapest but people say they have the worst beer. Augustiner is probably the most widely drank beer among the locals so is usually touted as the nicest. If you dont know the local beers you can get them cheaply in the supermarket to have a taste before the Oktoberfest so you know if there are any tents you want to specifically target or avoid.
Radler is like a shandy and would be an option if you arent wanting to drink a lot or are wanting to spend less money.
The food in the tents is expensive and no different than what is served in the traditional bavarian restaurants in Munich. If you are looking to keep costs down I would reccommend having a meal in one of those rather than at the Oktoberfest. Plenty of them to choose from with good food and fair prices and more options than what is available at the Oktoberfest.
Locals call it Wies'n so if you hear people saying that or see the signs pointing to Wies'n thats where you need to go.
There is a section called old oktoberfest which is more traditional and generally less busy because you have to pay and entrance fee.