You can't add multiple Steam accounts to the same client. Each Steam account requires its own separate client. However, you can easily switch between multiple Steam accounts on the same computer. Here's how:
- Log out of your current Steam account. This can be done by clicking on your username in the top right corner of the Steam client and selecting "Log Out".
- Launch the Steam client.
- Log in with your desired Steam account.
Alternatively, you can use multiple Steam clients:
- Download and install a separate Steam client for each account. You can download the Steam client from the official website.
- Launch each Steam client separately.
- Log in to each Steam client with its corresponding account.
This allows you to have multiple Steam accounts running simultaneously on the same computer, with each account having its own separate library, friends list, and settings.