Checkpoints are collection periods to record assessment data, there are maximum of 7 a year; one for Baseline and then one for each half term. You do not have to use all the Checkpoints, if you only wish to assess termly.
Checkpoints for Steps are hardcoded into the ScholarPack software, if you are using this assessment platform you will not need to set up any Checkpoints.
If you are using the summative markbook you may see that you are unable to change the checkpoint you want to enter data for, this is because the system by default locks the checkpoint to the term you are in. If you need flexibility to enter data in retrospectively you can change the systems setting by going to Admin > Config > Steps Assessment Config.
You will see a column called Lock Checkpoints KS1+KS2, you will need to click Edit, then change ths to No.