how do i sign into icloud on my desk top?

See the articles https://support.apple.com/guide/macbook-pro-16-inch/set-up-apd831707cb3/2019/mac/10.15.1

https://support.apple.com/en-in/guide/icloud/mmfc0f1e2a/icloud

If you are not having an Apple ID create it https://support.apple.com/en-in/HT204316

And then sign in https://support.apple.com/en-us/HT204053

You have not been specific. On the web? On a Mac, if so which version of macOS? On a PC?

If you mean iCloud on the web which is suggested by your question, on a browser go to www.icloud.com and enter your credentials.

If you mean signing in to iCloud services on your Mac go to System Preferences > Apple ID

Windows uses can install iCloud for Windows.