Universities often ask you to send them two or three letters of recommendation. The best way is to ask a professor in whose class you have been successful, had a good theoretical or practical project, or participated in their research activities.
[…]

Some people prepare a letter of recommendation and ask the advisor to send that to the destination university. This is by no means advisable because, if you are not able to write a professional text, the decision makers of the destination university cannot properly judge your abilities and you may lose your chance of admission. […]