It has been a while since I published anything for year 1, so here are a couple of pages on understanding subtraction. They look very straightforward but there are a number of concepts involved here:
Firstly, understanding that the phrase, ‘How many are left’ .
Secondly, relating subtraction to ‘taking away’.
Thirdly, the answer can be found by counting up from a number.
Fourthly, the answer can be found by counting back from the larger number.
Finally, that the minus sign means subtract.
Thanks to urbrainy.com for letting me use these two pages.