Hi Esmé!
To start testing some of the features of SquareSpace, try adding a new ‘section’ below this one. To begin, select ‘add a blank section’ first, rather than any of the pre-made layouts.
Once you have your new section, add a text block (like this one), and get to grips with how the sizing snaps to the underlying ‘grid’ of your website (this is what allows everything to resize responsively to different screen sizes). Add some text using the various heading and paragraph styles I have set up.
Then, hover over the section and click ‘Edit section'. Go to the ‘Colours’ tab and try applying the various different colour themes, to see how the text elements automatically change through various combinations of your brand colours that I have selected to offer optimum legibility and balance.