If you don't want to buy bitcoin directly you can also chose to trade it. Trading basically means that you predict the future movement of the market. There are many websites and mobile apps that offer trading so you can just search the appstore or the internet for bitcoin trading.
But I want to tell you about the website that I use as I think that it has many advantages.
eToro is a social investing platform. This means that you can see what other traders are doing and look at their open trades and trade history. They also offer much free learning material about trading, which gives you the opportunity to understand the basics fast and extend your knowledge.
But in my opinion the best feature of eToro is that you can copy other traders. This means that you can choose a trader with good stats that you trust and the amount of money you want to use to copy his trades. Then all trades done by the experienced trader will be executed on your account as well. So you can profit from the knowledge of other traders and do not have to do all the research work yourself.
Investing involves the risk of losing your invested money! Stay safe and only invest amounts of money that you can live without. The past performance of any trader or currency, stock, etc is not indicative for future performance!