Open table in Design View, select the column, and change two properties:
Change Required to Yes.
Change Allow Zero Length to No.
This won't work with AutoNumber data type, but for all others it will.
It sounds like you are wanting to set up the database such that people can input data. If so, they should not really be inputting directly into a table. There should be an input form that checks the data before adding it to the data table. That form could also enforce any required fields.