Here is the bit you want about the form open/close stuff.
Create a form, with two command buttons. "Enter New Record" and "Search for an Existing Record." would be the caption, but the names lets do this.
fmrMain is going to be this "Main Menu" form.
cmdNew = "Enter New Record"
cmdExisting = "Search for an Existing Record."
Assuming you have this "Main Menu" form set to open on load. This is the code you would add under the form. In Alt+f11, or the onclick event of the button in properties.
Code:
Sub cmdNew_Click()
DoCmd.close acForm, Me.Name
DoCmd.OpenForm " ~ Insert form used to enter new record here ~", acNormal
Sub cmdExisting_Click()
DoCmd.close acForm, Me.Name
DoCmd.OpenForm " ~ Insert form used to read an existing record here ~", acNormal
And from those other forms, you just do it in reverse.