If you are just going to buy your first cryptocurrency then I will advice you to stsrt it with Bitcoin even if you buy bitcoins worth of $100 is better than investing into cheap altcoins which may not have potential and its really hard to choose which altcoins to invest for a beginner. And keep yourself updated with crypto related news and information by keep yourself active on this platform.
The initial choice to buy Bitcoin is not a bad choice, because Bitcoin is the most valuable Coin today. But for some other altcoins it doesn't seem that difficult to choose.
Just have a look at some of the top lists on Coinmarketcap such as the top 10 recommended altcoins list like ETH, BNB, XRP and other coins.
The most important thing before investing is reading market movements. A beginner must also know when is the right time to invest. Basic knowledge of initial investment and trading knowledge will be required.