So for being a beginner you're off to a good start by designing two separate subroutines that you can confirm work and then integrating. That's the basic approach that will save you headache after headache when things get more complicated. So to answer your direct question on how to integrate the two, I'd recommend doing something like this
Sub BasicFindGSV()
Dim movement_type_code As Variant
Dim total_gsv As Variant
movement_type_code = "Rec"
total_gsv = Application.WorksheetFunction.VLookup(movement_type_code, Sheet1.Range("C2:H25"), 2, False)
AssignValueToBlankCell (total_gsv)
End Sub
Sub AssignValueToBlankCell(ByVal v As Variant)
Dim Sheet2 As Worksheet
Set Sheet2 = ActiveSheet
For Each cell In Sheet2.Columns(2).Cells
If IsEmpty(cell) = True Then cell.Value2 = v
Next cell
End Sub
That being said, as Macro Man points out, you can knock out the exact same functionality your asking for with a one liner. Keeping the operational steps separate (so actually a two liner now) would look like this.
Sub FindGSV()
AssignValueToBlankCell WorksheetFunction.VLookup("Rec", Sheet1.Range("C2:H25"), 2, False)
End Sub
Sub AssignValueToBlankCell(ByVal v As Variant)
Sheet3.Range("B" & Rows.Count).End(xlUp).Offset(1, 0).Value2 = v
End Sub
Like I said, if you plan to continue development with this, it's usually a good idea to design your code with independent operations the way you already have begun to. You can build off of this by passing worksheets, ranges, columns, or other useful parameters as arguments to a predefined task or subroutine.
Also, notice that I use Value2 instead of Value. I notice you're retrieving a currency value, so there's actually a small difference between the two. Value2 gives you the more accurate number behind a currency formatted value (although probably unnecessary) and is also faster (although probably negligible in this case). Just something to be aware of though.
Also, I noticed your use of worksheet objects kind of strange, so I thought it'd help to mentioned that you can select a worksheet object by it's object name, it's name property (with sheets() or worksheets()), index number (with sheets() or worksheets()), or the "Active" prefix. It's important to note that what you're doing in your one subroutine is reassigning the reference of the Sheet2 object to your active sheet, which means it may end up being any sheet. This demonstrates the issue:
Sub SheetSelectDemo()
Dim Sheet2 As Worksheet
Set Sheet2 = Sheets(1)
MsgBox "The sheet object named Sheet2 has a name property equal to " & Worksheets(Sheet2.Name).Name & " and has an index of " & Worksheets(Sheet2.Index).Index & "."
End Sub
You can view and change the name of a sheet object, as well as it's name property (which is different) here...
The name property is what you see and change in the worksheet tab in Excel, but once again this is not the same as the object name. You can also change these things programmatically.
Worksheets("sheet2").Range("B" & Rows.count).End(xlUp).Offset (1) = total_gsv
It will find the next empty cell and place the value of tota_gsv into that cell. – Scott Craner