Dear Sabrina,
Once you create your list of sampling point data, you can use it as a code list (it's called sampling_design among the list of available code lists in the code attribute editor).
Also, you can define extra columns; all the columns with a name different from level1_code, level2_code, level3_code, x, y, srs_id will be considered as extra info column and you can use it in your expressions or in a calculated attribute with this function:
idm:samplingPointData('extra_info_column_name', plot_num)
You can have a look to the functions used in Collect by clicking on the button close to every expression text box and we will add soon a detailed documentation about these functions in the Collect manual.
Many thanks,
Open Foris Team