Squid is a proxy that runs on your network: your programs point to it and it forwards the connection. Here it sits between your machines and the address you bought.
How to point Squid at our address
Use the delivered address with the protocol port, 20001 for HTTP or 20481 for SOCKS5, plus the username and password from your order. Accounts using IP authentication can leave username and password out.
Then allow your local network in the access rules and check with the proxy tester tool: the IP shown must be the purchased address, not your own connection.