There are fees involved with buying from Coinbase and some types of trading on Coinbase Pro (which can in cases get lower as you buy / trade more). Other exchanges have better rates than Coinbase (for example Coinbase Pro itself has better rates). However, rarely do exchanges have a better fee schedule than Coinbase Pro. In other words, when using Coinbase specifically, you’ll pay a little bit more than market price (or sell for a bit less than market price) and pay a small fee when trading on Coinbase (this is a trade-off for ease of use). NOTES: To be clear, there are essentially two sets of fees when you buy with Coinbase. One is them charging you more per coin than on Coinbase Pro or other exchanges; the other is an actual fee (currently paid in crypto, not USD, so if you buy 1 Ether, you get a little less than 1 Ether but pay the market price). That is the price you pay for them doing all the work and taking the risk of the price changing quickly when you buy. Not a reason not to use Coinbase and only use Coinbase Pro every time, but it is something to keep in the back of your mind if you start making lots of buys.
A cryptocurrency (or crypto currency) is a digital asset designed to work as a medium of exchange that uses strong cryptography to secure financial transactions, control the creation of additional units, and verify the transfer of assets. Cryptocurrencies use decentralized control as opposed to centralized digital currency and central banking systems.