A site is the container everything is store in — captures, processing settings, exports. Creating one and uploading into it is a single wizard.

The Create Site wizard. The stepper in the grey bar shows the whole path: General, Upload captures, Base Stations, Review.
Press + Site on the Dashboard.

The General step asks for:
|
Site name required |
The identifier for this grouping of captures. What your team will search for. |
|
Description optional |
Additional site details you want to add. |
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Folder optional |
Where the site lives. Reads No folders available until you've made one. |
|
Tags optional |
Pick from the org's tags. You can't invent one here — Admins manage the list. |
|
Coordinate system Auto / Custom |
Every capture assigned to the site is processed against the site's CRS. Auto will default to UTM projection and meters as the units. Use Custom when you know what coordinate system you want to use. See note below |
From General you can finish there — Create site makes an empty site — or continue through Add Captures into the same upload flow described in Starting Captures Processing.
The coordinate system is sticky. Once captures have been processed against the site's CRS, you cannot change it without reprocessing them. Get it right before the first upload if the job needs a specific projection.