PuTTY localhost

"localhost" refers to the current PC, so PuTTY is trying to connect to an SSH service on the same PC that it is running on - your Windows PC, which probably isn't running an SSH service. If you're trying to connect to some other computer on your network, you need to specify the name or IP address of that other computer, instead of localhost.

PuTTy / SSH is a secure way to connect from one computer to another across a possibly insecure network, and run a command-line shell on the remote computer (usually the remote computer is a Linux or Unix computer, and usually the shell is bash or something similar). It's not normally necessary to use this to connect to the same computer, and it's also not normal to run SSH or bash on a Windows PC. The normal way to get to a command-line shell on a Windows PC is just run CMD.EXE or PowerShell.exe - no network tools are required. If you do want to use bash locally on your Windows PC, you can do with without PuTTY or SSH.

Unless you have an unusual situation, running both PuTTy and SSH on the same Windows PC is probably not the solution you want. You may be better off asking another question, and describing what it is you're trying to do.