To get started head over to "Set Up" > "Availability". Here you will be presented with a list of staff members. Pick either yourself or one of your colleagues, in case you're setting up working hours for your staff.
To add new working hours or to edit existing ones, simply click on the card under the date.
You will now be presented with a new window on the right hand side. Here you can add new working hours, pick which locations you work from and if you want to apply this to all future dates or to only apply it to a specific day.
Please be aware that on the Free/Basic/Micro plan you can only set working hours at "All Locations". To be able to select a specific location you will need to be on the Grow/Pro plan or above.