help with having specific dimensions on a box

You can insert a text box via Insert tab >Text Box > Draw Text Box. 

Select the text box and use the size controls on the Shape Format tab to set the desired height and width. The dimensions will be in your system default unit of measurement, but you can specify values in points, if you wish. Word will convert them for you. 

 

How about using a shape:

 

1. Insert a Rectangle
• Go to the Insert tab
• Click Shapes → choose Rectangle
• Click and drag anywhere on the page
2. Set Exact Dimensions
• Right-click the rectangle → choose Size and Position
• Under the Size tab:
• Set Height to 3.5" and Width to 2.5"
• Click OK
3. Optional Styling
• Add a border: Right-click → Format Shape → Line → choose color and thickness
• Add text: Right-click → Add Text