WordPress.com site eats code

I am not tech savvy at all.

I keep trying to add a simple bit of pay pal coded html for a drop down pay now button, nothing fancy.
I copy the code.

I open the word press blog page (from the admin page) I want to add the code to making sure the html or text tab is where I am pasting the code.

I take a peek on the “visual” tab and see my happy little drop down pay now button.

I click the publish/ update button.

And then all of the little pearls of code are gone except for a few lines of leftover code and the information of what I wanted in the drop down. It’s as if the update button gobbled the code up.

I have searched for an answer but I can’t find one yet. How can I stop the madness?