ETH derives its value from supply and demand, like all other cryptocurrencies. An important factor that influences the demand for ETH is that ETH is needed to cover for all computational fees done on the Ethereum network. This means that any digital asset or smart contract using the Ethereum network requires ETH to operate, and its users are required to own ETH in order to make transactions.
This means that ETH benefits from all other digital assets on the Ethereum network. Therefore, the price of ETH can be correlated to the popularity of the Ethereum network, although there are many other factors present that influence price.
ETH is available on most cryptocurrency exchanges and can often be traded for fiat currency directly. It can also be traded privately with a trusted counterparty. In some countries, ETH can be purchased through cryptocurrency ATMs.
Alternatively, you could contribute to the Ethereum network by mining, and earn some ETH coins in return. This method will not be viable for everyone, as cryptocurrency mining requires a substantial upfront investment.
Having in mind the number of crypto assets and decentralized applications based on the Ethereum network, investing in ETH has the potential to be very profitable. Using any Ethereum-based digital asset or decentralized applications requires using ETH as well, which can help boost demand and therefore also the price of ETH.
However, as the whole crypto market is generally considered highly volatile, investing large amounts of funds is not recommended without proper education and a thorough assessment of the associated risks. As prices tend to change rapidly, and small mistakes can lead to big losses, cryptocurrencies are generally seen as high-risk investments.