The Remote desktop action opens an interactive RDP session to the selected server using the standard Microsoft client (mstsc.exe).

Select one server on the Servers tab, then:
A new mstsc.exe window opens connected to the server's hostname or IP from the computer list entry. If the entry has explicit credentials stored, they are passed to the client; otherwise Windows handles the credentials prompt as usual.
The User sessions tab also has a Connect action on the row's context menu. Use it when you want to start a new Remote Desktop session as a specific user without typing the password into the standard Windows credential prompt.
What you see:
mstsc.exe opens against the server.What happens under the hood:
TERMSRV/<server>, using the cmdkey command. This is the same store the Remote Desktop client looks at when it needs credentials for a server.mstsc.exe /v:<server> (with /multimon if Connect with /multimon option is enabled in the Terminal Services preferences). mstsc picks up the stashed credential automatically and signs in.cmdkey /delete, so the password does not stay in the Windows Credential Manager after the session is launched. The RDP window itself keeps running until you close it.Notes:
To shadow a running session instead of opening a new one, use Shadowing a user.
From the User sessions tab, use the Connect action on the row's context menu (described above) to open an RDP session as the selected user. On the Processes tab, the Remote desktop action on a process row opens an RDP session to the row's server using the standard mstsc.exe flow.
Terminal Services Manager does not embed an RDP client. The session runs in the standard Microsoft mstsc.exe window; closing that window ends the session. Settings such as full-screen, multi-monitor, drive redirection, and clipboard sharing are taken from the saved .rdp profile or the current mstsc.exe defaults; they are not configurable from this program.