Firstly, navigate to the settings page by clicking on the Profile tab at the bottom of the sidebar and then clicking Settings [Below].

Next, Click on the + Create button on the top left-hand side of the screen ...

A pop-up box appears [Below], with 2 Fields to complete,

1. Tag Name: How the tag will appear in Account/Contact records, Playbook setting etc

2. For: Select whether this Tag will apply to either Contacts OR Accounts.

You can decide whether to apply a color to the Tag, this can be a useful visual shorthand to indicate if this is a positive or negative Tag.