What is your table structure?  Field property.
What have you tried?

Need more info please.

What have you tried?
Screenshots?

Filter Records

Look for course number.       (This is working fine)

Course Number:
  Field Name: Tbl_Trn_1_CourseNumber
   Data Type:  Short Text

Private Sub FindCourse_Click()
Dim S As String
    S = InputBox("Please Enter Value", "Find Course")   '(i.e. Field to use as default)
    If S = " " Then Exit Sub
    
    Me.Filter = "Tbl_Trn_1_CourseNumber  = """ & S & """"
    Me.FilterOn = True
End Sub
--------------------------------------------------------------------------------------------
Look for Group Code.       (This is not working)

Group Number:
   Field Name: Tbl_Trn_1_CourseGroup
    Data Type: Number (Single)


Private Sub FindGroup_Click()
    Dim S As Single
   S = InputBox("Please Enter Value", "Find Course Group")   '(i.e. Field to use as default)
  If IsNull(S) Then MsgBox ("Fill in a number")
   Exit Sub
MsgBox ("Passed")

    Me.Filter = "Tbl_Trn_1_CourseGroup  =  S "
    Me.FilterOn = True
  End Sub

Input Boxes always return a String. I would store the value in a String and then convert to a Single (storing the value in another variable). Also, in the Me.Filter command you had the variable inside the quotes. The filter method was trying to set your field name equal to the character "S" instead of the value of the variable.

Here is how I would write this.

    Dim S As String, Num As Single
    
    S = InputBox("Please Enter Value", "Find Course Group")   '(i.e. Field to use as default)
    If StrPtr(S) = 0 Then Exit Sub 'the user clicked cancel
    If S <> "" Then
        Num = CSng(S)   'convert S to single, store in Num
    Else
        MsgBox ("Fill in a number")
        Exit Sub
    End If
    MsgBox ("Passed")

    Me.Filter = "Tbl_Trn_1_CourseGroup=" & Num
    Me.FilterOn = True

In addition to what Kevin said, I also recommend that you discard the use of Single.  While it will work it really can confuse the issue trying to remember the data types in your code.
As you progress through the courses you will see that Richard only uses 5.
Long Integer, Short Text (string), Double (for decimals), Long Text, and logical or boolean (Yes / No).

Space and speed are not the issue that they once were so there really isn't a need to use Single. The advantage is if you ever do go over the limit you don't have to go back and change code.

I don't recall if there is a video specifically about Data Types but I'm sure Richard  covered this early on in the Beginner series.

Take a look at the Type Conversion video for how to convert the text to differing data types.

Thanks very much guys.