Missive offers two kinds of labels: email labels, which sync with your email accounts, and organization labels, which are tied to your Missive organization.
Email labels are synced back and forth between your email account (Gmail, Office 365, IMAP) and Missive. Coworkers you give full access to your email account on Missive will have access to all the labels of that email account.
Organization labels are Missive-only labels that are not synced to an email account. An organization label can be applied to any conversation, whether it's an email, SMS, social media or an internal chat conversation. Organization labels have advanced settings and use cases you can learn more about here.
Organization labels are more flexible than email labels, but they don't sync back to your email server. Here is a table summarizing all the differences between the two:
Creating labels is simple, you can do it from the Settings > Labels. Or you can create them when viewing a conversation, just click on the label icon at the top of the conversation, like this:
Editing (color, description, etc.) and deleting labels is done from Settings > Labels or by right-clicking on one in the sidebar and selecting the Edit label option.
To open and keep a label in the sidebar, click the + More menu then find and select that label. If you prefer to only navigate to a label without keeping it open in the sidebar, you can press the Option key while clicking on it.
You can also quickly find and open labels using the search input at the top of the conversation list (Command + F to select the input), just type the first few characters of your labels. The same Option trick applies if you want to navigate to the label without pinning it to your sidebar.
Lastly, you can use the Command Bar menu by typing Command + E and searching for the Go to label option: