It's funny you mention this because I've got something very similar coming out soon as both a TechHelp video and a Developer lesson. I'll be showing a practical way to map out tables, fields, and relationships before you get too far into building the database.

In the meantime, you don't necessarily need a special database-design program. Access itself has a built-in Relationships window, which is perfectly fine once you have created your tables. You can arrange the tables visually and create the joins between primary and foreign keys.

For planning before you build anything, diagrams.net (formerly draw.io) is a good free option. You can create a box for each table, list its fields, and draw lines between related tables. Even paper and pencil works at this stage. The important thing is thinking through the entities first: Customers, Orders, Products, Employees, etc., and then determining how they relate.

Since your data is currently in Excel, I would strongly recommend not just importing each spreadsheet directly and calling it done. Take the time to identify repeating information and split it into proper related tables. For example, customer information should normally be in CustomerT once, not repeated on every order row. That is where a diagram really helps you see the structure before you start building forms, reports, and automation on top of it.

You're definitely at the right point to make the move. A little planning now can save a lot of database surgery later.

If you follow Richards courses and design your database the way he teaches it... you will be able to expand your database beyond your initial plans and things will just work.  Where it becomes more difficult is when you make bad design decisions that end up creating problems later on.

-Raymond

Listen to Raymond. He's smart. :)

I love using Mermaid to diagram almost anything.

An ER might be something you can use.

https://mermaid.ai/open-source/syntax/entityRelationshipDiagram.html

If you're looking to move to MS SQL then you could also use https://www.drawdb.app/ amongst many others.