Hey, At first you should create a bitcoin walltet. There are so many ledger in market but i prefer blockchain wallet. So create a account through blockchain.
You must should study about bitcoin also note that you should analysis market trend of bitcoin or study previous history day to day or month to month.

If you have idle money then you can invest through your blockchain wallet and keep your eye o market. When price will be increased then sell your bitcoin at a higher profit.

Remember one thing never buy  bitcoin or any other cryptos to it's peak point. Take your own time and wait for decreasing price then buy.