If you are a beginner I recommend buying ETH as reasonable. Because ETH is second only to Bitcoin. on the other hand, ETH is rebounding but not yet highly potential. You can make an account and invest in a Binance exchange I find this transaction page very good and relatively safe.
Second only by market cap and trading volume. This positions does not mean anything. With enough resources and demand any altcoin can get a second place. Just look on Polkadot. No one knew about it this spring, and thanks to a boom it is now among top10. So the place of altcoin in top is not something to pay a lot of attention on. But, Ethereum can be a safe long term investment. No doubt of that.