Q: Car is squealing but not when a/c is off, no power when pressing on gas, hesitates to get fuel & has horrible gas mileage& more

My car only squeals sometimes but will stop if i turn the A/C off. When i press on the gas it doesnt have power to go, it will eventually just randomly speed up after not having power. I need to know if it may be serpentine belt (squealing & what not), throttle position sensor (for the lack of power) or if i just got a tune up with new spark plugs id be okay. I just bought this car a few days ago & nothing was wrong with it when i test drove it. I should get good gas mileage but i have only drove almost 200 miles. Not even that much. Ive drove it to work 3 times. (started with a full tank) & im almost on E. Can spark plugs fix most of the issue when it comes to gas & power? I know the squealing is from a belt i just dont know whats making it happen. I will be pressing a lot on gas & it doesnt accelerate til minutes later. I do need to adjust my timing since my car idles & shakes when its in gear not when in park. I just need to talk on phone for advice. Theres multiple problems

My car has 244000 miles.
My car has an automatic transmission.