Well, Alarms have the following severity levels:
So, if an alarm is Green it can be considered informational and no action needed. For a alarm in Yellow, its a warning and might need some attention followed by action. Whereas for the alarms in Red, they need immediate attention & action depending on the situation.
You could look for alarms either at vCenter level, Cluster or ESXi Host level.
For vCenter level: Choose your vCenter > Monitor > Issues and Alarms > Triggered Alarms
For Cluster level: Choose your Cluster > Monitor > Issues and Alarms > Triggered Alarms
For ESXi Host level: Choose your Host > Monitor > Issues and Alarms > Triggered Alarms
Reference - Monitoring Events, Alarms, and Automated Actions (vmware.com)