I agree with David H. We would usually say "I want to get that", Obtain is definitely more formal. When I hear acquire my assumptions is there was a purchase. I went to the kitchen and obtained an apple. I went to the store and acquired an apple. That would be formal. I would more naturally say I got an apple, or I bought an apple.

They are basically the same I would say. There are some time we use on and some times we use the other but they are mostly based on strength of collocations (which words work better with them). If you want to sound natural and it is not a formal context, use 'get' more than these.

I agree with David and Todd. These are both formal words which we rarely use in everyday English. I also agree that 'obtain' is a more formal way of saying 'get' : you might see it written instructions or on official notices. 'Acquire' suggests a more complex process, perhaps a purchase, inheritance ..or even theft... of an item. As David says, the difference is mainly an issue of collocation. Don't look for explanations or dictionary definitions. Just read and listen to as much English as you can, and you'll get a feel for what 'sounds natural'.