Without researching it, I feel they are all relatively the same, however, used in different circumstances. "get" seems to be the most casual and common and can always replace "gain" and "obtain". Ex: I get cold easily. I get hot when I wear jackets. I get my next paycheck Friday. I gained valuable experience (could also say "I got"). "Gain" is slightly more formal, and something that happens over time. I gained five pounds of muscle last year. It is hard to obtain a good paying job these days. "Obtain" would be most formal, any sentence I thought of with "obtain" could be replaced with "get/ got". To "obtain" something is harder to do then to "get something". May involve a procedure or something difficult to do. Sorry.... this is hard to explain :). I think familiarity with these words will come with experience. If you're doubting how to use these words, you can probably just write "get". Gain and obtain are not as interchangeable.

"Obtain" is to come into possession of something, usually through some action or effort. "Attain" is to reach a certain thing or goal and could also mean obtain. The two terms are very close and could be used as synonyms but "obtain" slightly implies more effort being made toward a goal. Three examples: After running the gauntlet of poison darts, land mines, and pendulums, the hero obtained his prize at the end. When movie stars and rock stars die young they often attain superstar status. With enough game experience you will eventually attain level ten. You see the difference? Usually, you have to put forth more effort in "obtaining" something. This may or may not be the case with "attain." In the second sentence above, no effort was made other than death. In sentence three some effort was made. __________________________________________________ "Gain" is different. One can gain something with effort or without any effort whatsoever. Gain can be applied any time one has come into possession of something or benefited from something. It does not matter if it took effort. Examples(one is an old cliche'): When a man's daughter get's married, he does not lose a daughter; he gains a son-in-law. You lost the money and I found it. Your loss is my gain. Through good education, you will gain a big advantage over many people. Get- neutral form of the other words https://www.quora.com/Whats-the-difference-between-obtain-attain-and-gain

Look at the etymology: www.etymonline.com The meaning will be as clear as day! :D