need users to enter data from userform only, not directly into cells

First, thanks for being patient with me, this is my first post.
I took excell (Made an A) in Jr. college in 2002, have not used it since. Took on a project at work to teach myself vba, have almost finished it with a lot of help from reading this forum. I started simple, and as I read someone else say, I got addicted to improving it.

My last problem to solve, which has stumped me, is how can I make it where the user can only enter data from a userform, not select the cell directly. I am leaning toward locking the cells, protecting the sheet, and having the userform unlock or unprotect when opening, and relock when closing. Is this my best solution and if so how do I go about it. The sheet needs to be protected anyway to keep users from resizing/changing formats such as column widths and heights. The people that will be using it cannot help thenmselves, they like to change everything
Please be gentle because I have to struggle to understand the basics, especially understanding where to place code snippets once I have them. Thank you in advance. I am using Excel 2007

Thanks for your assistance. However, I went to the link you provided and did not find an answer. I have already completed the userforms, etc. They are all working ok. I just need to lock it down so that the only way to enter data into the sheet is with the userform. If the answer was there and I missed it I am sorry.