Menu items or buttons that a teammate has but you don't? It comes down to two things: your role, and which add-ons are on.
Your role
Your role controls what you can see and do. A Technician, for example, works their visits but doesn't create jobs or change company settings — so those options simply don't appear. If you need access to something, ask an Admin to adjust your role. See What are user roles and permissions?
Add-ons
Some features are add-ons that have to be turned on — like the Client Portal, Service Plans, Timesheets, or Text Messaging. If a whole feature is missing, it may not be enabled for your company. An Admin can turn it on from Add-ons. See Turn on add-ons and integrations.
Tip: Not sure which it is? If a teammate with a higher role sees the feature, it's a role difference. If nobody does, it's probably an add-on that isn't turned on.