For one, don't worry about looking like a dumbass. These places have "budtenders" who are there to help you and who are very used to noobs coming in and being overwhelmed. I'd say to feel prepared, think about these 3 questions:
1) How do you want to consume it? Your options will be "flower" which is weed that you would roll and smoke (they also have pre-rolled joints), vape pens/cartridges, or edibles. If you want to do edibles, you will have options like gummies, other candies like chocolate, and drinkables.
2) What experience are you wanting? Mainly are you looking to feel euphoric or relaxed? The experience you want will influence what type, or strain, of weed you choose. Generally, sativa is more euphoric and indica is more relaxed. They also have hybrid options.
3) How strong are you looking to go? The gummies/candies you usually have either 5mg or 10mg of THC options, and the packages usually have 100 total, so either 20 5mg or 10 10mg. I kind of like the 5mg options in the gummies to help control and keep a solid buzz. Similarly, the 10mg beverages you can sip a bit and have a gradual onset.
Don't feel like you need to enter the dispensary having these answered 100%, but if you have at least thought about them, that will help your convo with the budtender be as productive as possible.