Yes, you can earn from mobile apps but don't expect that you will earn a lot from it. There are some legit apps that can be downloaded on app store or play store but most of it are scams. One advice though is search and review first the app before downloading it. I am currently using instagc which is a website that will pay you by answering surveys and by downloading mobile apps mostly games. You will be earning points by just downloading mobile apps. But don't just rely on it because again it will not give you a $1 in just a day. Honestly, I haven't redeem my earnings yet on instagc since I am still working to get the minimum points required to withdraw money from it. Consider it as a free bonus, like a small extra income. You can also try playing videos on snuckls and baymack. Who knows you will win a thousand dollars from it. I am doing it while I'm doing other stuff on my laptop. I am always winning, most of the time I get $0.02 cents. I know it's very small but then again, who knows we can win the jackpot, right? Besides, you didn't put a money or investment on it. Nothing to lose. But, don't do this for a living because it will not make you rich.
By the way, I just downloaded the snapwire app wherein we can sell our taken pics from our phone or other cameras. It is legit! If you love taking pictures then I suggest download the app and enjoy posting your pictures and sell them to buyers.