First of all, keep in mind that the wallet only handles yous coins, the coins will never be "in" your wallet.
This means that anybody who has a copy of your wallet, or a copy of your wallet's seed, or a copy of the private keys of your coins, will be able to spend them.
This may sound scary, but it simply means that you have to be careful with the wallet/seed/backups (yes, please save the seed onto paper and keep it safe).
I use Electrum on my laptop. But if you want to do so, please make sure you download it from https://electrum.org and verify it ( https://bitcoinelectrum.com/how-to-verify-your-electrum-download/ )
If you want to use Electrum on mobile, also go to https://electrum.org and the download page will contain link to google play. You need this kind of precautions because the internet is full of COPIES that may look like the correct wallet, but will just steal your wallet's details and your coins.
If you buy 50$ worth of Bitcoin, then you should know that bitcoin transfers cost money (pretty much lately) and also the exchanges ask pretty big withdrawal fees. So if you buy from an exchange and not your friend, you may want to check the fees and consider keeping the money there until you have more and it worth withdrawing. Also keep in mind that you will need KYC/documents on most exchanges.
If you plan to buy (in time) more bitcoin, you may consider buying a hardware wallet.