warning: database file for ‘core’ does not exist (use ‘-Sy’ to download)
warning: database file for ‘extra’ does not exist (use ‘-Sy’ to download)
warning: database file for ‘community’ does not exist (use ‘-Sy’ to download)
warning: database file for ‘multilib’ does not exist (use ‘-Sy’ to download)
error: target not found: steam
Your running an arch based distro which is a rolling release, it’s important to keep your system upto date and always update when installing a package. If you are new to manjaro then keep an eye on the announcement threads as all updates will be posted there and any potential hazards that may occur