Check the Reading & Writing Cell Values guide.
For example if you want to read from a single range you can use:
GET https://sheets.googleapis.com/v4/spreadsheets/spreadsheet_id/values/range
-sheetId is used frequently in the Sheets API to specify which sheet is being read
or updated. In the Sheets UI, you can find the sheetId of the open
sheet in the spreadsheet URL, as the value of the gid parameter. The
following shows the structure of the URL and where sheetId can be
found:
https://docs.google.com/spreadsheets/d/spreadsheetId/edit#gid=sheetId
When I did this ins JS REST call it looked something like this:
xhr.open('GET','https://sheets.googleapis.com/v4/spreadsheets/spreadsheetId/values/Sheet1!B3:B71', true);
Here, I'm trying to read values from B3 to B71. Read more on A1 notation about this.
To do this in PHP, check the php-google-spreadsheet-client.