For example, Freewallet doesn't support SHIBA INU and this token is based on Ethereum. Can I use my Ethereum address to receive SHIBA INU?
As far as I know Shiba Inu is an ERC20 token, so receiving it using your ETH address(assuming this is not from an exchange) is ok. But in order to access this token, you must use an ERC20 compatible wallet such as myetherwallet.com, metamask or any wallet app that is erc20 compatible.
If in my Ethereum wallet, I have some Ethereum and use my Ethereum address to receive SHIBA INU, then these coins do not combine?
If you have the private key of or the seed phrases or the json file of the address then you can just import your wallet address to a wallet that supports ERC20 token to view your SHIBA INU token.
Here is the known ERC20 compatible wallet (just found an article about it) but I recommend Myetherwallet, Mist or Metamask since I use them without any issue.
Thank you, but how about my questions ==> If in my Ethereum wallet, I have some Ethereum and use my Ethereum address to receive SHIBA INU, then these coins do not combine?
It won't combine since they have different contract address. You can see your ETH balance and also your Shiba Inu. See this screenshot of metamask