Number formatted as a text

Hi

I entered '10 (apostrophe first then 10) in cell A1. The number went to the left hand side of the cell with green triangle at the upper corner of the cell. When I tried =sum(A1), I got 0.

Then I changed cell A2 format from general to Text and then entered 10 in cell A2. The number went to the left hand side of the cell but without green triangle. When I tried =sum(A2) I got 10

What is the difference between these 2 scenarios? Why the first one the sum(A1) gave me 0 and the second one sum(A2) gave me 10?

Thank you very much

Thank you very much for your reply. For the second instance, if I had the number there, wont that change the number to text because the cell is formatted as a text? I have hard time to understand the difference. Thank you very much.

Thank you very much for your help.