Help with selection and sub selection in Access

I’m trying to learn access to making tracking material orders for my job site much easier. I’ve created a table with categories, another with units of measuring those materials, and another that has the materials listed according to the category they fall into. I’ve set it up so that I get a drop down list for the category when I add a new material. I’ve even created a simple form to add more materials to the list. Now, I’ve created an order table to create orders for these materials, the date, how much, etc.

My ideal table would allow me to select a category in one column, and then select a material from a list in another column, that is restricted to only the materials associated with that category. I cannot figure out how to do this, and am finding it to be near impossible to find via google, and YouTube searches. Could someone please help me out?

Also, and this is a minor frustration, my forms always default to the first ID on a given table, and I need to press the button to add the new record, before adding a new one, so that it doesn’t overwrite that record. How do I default this form to select a new record each time?

Thanks so much!