Contextual actions in mobile/ios best practices

UX noob here...

I am trying to envision the vest way to present the user with actions he/she can perform in specific views of my iOS application.

Each view could have different actions.

I have seen a few apps (e.g., Google Calendar, Snapseed) implementing something similar to this:

Or alternatively this:

I there a particular name for these menus?

What is the best practice/approach for them in mobile apps?

Thanks!