The integration settings can be found at the far right of the main menu near the Settings dropdown.
From here you will be able to Add, Remove and Edit your integrations.
I will now go top-to-bottom an cover all the fields in the Integration Settings.
The left side will hold all of your already connected integration. You can sort them by their type or search for the via search field to the right.
Some integrations come types come with additional options that you can adjust by pressing the on "click here" near the edit text.
For instance, marketplace integrations can have their names changed, as well as custom logos added that appear on invoices for those sales channels. Return addresses can also be added, those appear on invoices as well.
To the right side you will see all of the integrations that you can add. You can sort them by their type or search for the via search field to the right.
Each integration has it's own short guide and a link to an extended guide
If you click to add a sales channel, you will find the short guide to the right and at the bottom you will find the link for more detailed instructions.