Importing Existing tokens on blockchain

I'm trying to create a Farming smart-contract. I'm completely new to solidity so i want to know if there's a way i can import an existing token from the blockchain, then call methods on that token's contract from my farm.

In tutorials I've seen, i see them create a "Fake token" then import it from same directory. My curiosity is; what if the token i want the users to deposit is already deployed to the network, how do i import that token so i can be able to call methods like transfer/transfer from on it.

To call someone else's token, you need to write an interface to this token

interface otherToken{
    // methods tokens example
    function method(uint param1, address param2) ... ; // The interface must match the methods of that token 

contract testContract{

    function callToken(address _token_address) public {
        otherToken(_token_address).method(param1, param2);