The RAIN token operates on Polygon network which uses POL as its gas token. This means you will need some POL in order to swap for RAIN. You'll also want to keep enough POL in your wallet to pay gas for future swaps and transfers.
You can purchase POL below from Flooz or from an exchange like MEXC, ChangeNow or cross-chain swaps on SushiSwap. You can also buy POL with a debit card via Metamask's Buy/Sell feature in the interface.
Metamask wallet is very easy to use and set up as a browser extension. After Metamask is installed, you can click "Add RAIN to Metamask" at the bottom of this page to switch to Polygon and add RAIN automatically. Alternatively, you can import RAIN manually using the contract address and Import Token feature. 0x8E677CA17065eD74675BC27bCaBadB7Eef10A292
Currently, RAIN is only available on a decentralized exchange as a RAIN/POL trading pair. This means you need to swap MATIC for the amount of RAIN you want. The easiest method is to use Flooz below or Metamask's built in swap feature, right in the interface. When using Metamask Swaps, click MATIC in your token list, then select RAIN as the token you wish to receive. An alternate option is to visit SushiSwap. SushiSwap requires an approval to spend your tokens. The approval takes some POL gas, after which you can swap into RAIN.