Excel 2013; User form to add data into looked up cells

[KrVa46]

Hello,

Unfortunately I'm no big VBE hero and I don't have a basis code to start from, but this is my question.

I created an excel document where I enter my expenses. All kinds of calculations happen and conditional formatting to get a quick view of budgets, results, expenses, ... It works fine and I'm happy with it.
Simplified layout in short:
[TABLE="width: 500"]
<tbody>[TR]
[TD]Budget[/TD]
[TD]Budget left[/TD]
[TD]Overview expenses[/TD]
[TD]January[/TD]
[TD]Februari[/TD]
[TD]March[/TD]
[/TR]
[TR]
[TD][/TD]
[TD][/TD]
[TD]Income[/TD]
[TD]+3000[/TD]
[TD]etc etc[/TD]
[TD][/TD]
[/TR]
[TR]
[TD][/TD]
[TD][/TD]
[TD]Rent[/TD]
[TD]-700[/TD]
[TD][/TD]
[TD][/TD]
[/TR]
[TR]
[TD]500[/TD]
[TD]column A - column D[/TD]
[TD]Shopping[/TD]
[TD]-50-100-40-...
[/TD]
[TD][/TD]
[TD][/TD]
[/TR]
[TR]
[TD][/TD]
[TD][/TD]
[TD]Grosseries[/TD]
[TD]-15.5-7.2-54.8-...
[/TD]
[TD][/TD]
[TD][/TD]
[/TR]
[TR]
[TD][/TD]
[TD][/TD]
[TD]Kids[/TD]
[TD]etc etc[/TD]
[TD][/TD]
[TD][/TD]
[/TR]
</tbody>[/TABLE]
In the comments of the cell I keep track of the date and where specifically I spent the money.

Now my dad is starting to use it too, but since he is way more inexperienced he keeps doing stuff wrong so that results aren't correct anymore. Even with locking cells he still manages to break it ...


I was thinking of creating a user form where you can only fill in the necessary information and it adds it for you to the correct cell. Something like:
Amount: "text field to add the $"
Month: "dropdown list with the months"
Detail: "dropdown list with the various categories)
Comment "text field to add the comment that needs to be added"

--

So I need a userform that:
- looks up a cell based on the input in the user form (month and category)
- adds the amount entered in the user form to the cell (not replacing previous data)
- adds the comment of the user form to the comment of the cell

I can troubleshoot existing forms and make them work for me, but I need a basis to start from and unfortunately I don't find anything like this already created.

Can someone help me with this?