I have simple userform with one multiline textbox and 6 checkboxes. My
problem is how to make that checking a checkbox will copy the textbox
value
to a new line without deleting the upper line. I tried various things
but
I
cant avoid the deletion of the upper line (especialy in the case of
more
then
one checked checkbox).

Copy the "textbox value" to a new line? Where is this new line going?

Did you, perhaps, mean to type "copy the CheckBox Caption property to the
bottom of the TextBox? If not, I think you will need to clarify what is
being copied and to where.

Before one of the checkboxes are checked the textbox has one line, with
for
example the word - apple. I am asking about the creation of new line
inside
the textbox that the word apple will appear with the word Juice for
example.
So the textbox after one checked checkbox will be:

apple
apple juice
apple pie (after the seconed checked checkbox)

Okay, now I think I see what you are asking. While you could concatenate new
text onto the old text like this...

TextBox1.Text = TextBox1 & vbCrLf & "Next Line"

it is more efficient to use the SelText property instead like this...

TextBox1.SelStart = Len(TextBox1.Text)
TextBox1.SelText = vbCrLf & "Juice"

A word about that first line. If, and this is a big if, the user can
possibly move the text cursor before you add your next line, then you need
it (because the new text is placed wherever the text cursor is located at).
On the other hand, if you were adding your text in a loop, you can omit it.
By the way, you can seed the TextBox with its first line by using the Text
property (you have to start somewhere<g).

Rick