You will need to log in to vCenter with the relevant privileges to be able to take snapshots. Snapshots do not work with:

• Virtual machines with RDMs in physical mode
• Virtual machines with PCI vSphere Direct Path I/O devices attached
• Virtual machines with Bus sharing enabled

Most importantly, snapshot do not replace backups. While it's advantageous in the short term, snapshots should not be allowed to prolong more than 72 hours, else it may have severe performance degradation. Also, more than 32 levels of snapshots on a virtual machine is not supported.