Hey!

I'm pretty new to bitcoins, i bought 0.05 BTC yesterday and 0.01 ETH. I keep Bitcoins in blockchain wallet and etherium in first mobile app wallet that came up in search.
0.05 Isn't much, but i plan to buy more in future. Are they safe? Should i make... Cold storage? If yes, how to make one/which one to download? Should i get usb drive just for that (if i will ever get more than one btc ofc)

Some more questions:

How to get bitcoins back from cold storage?
What are private keys? Public keys?
Why transaction fee is this large?
What is segwit (different topic but i saw it often in forum!)

Thanks!!