Try doing vs. try to do

Try + to + infinitive (try to do)
You try to do something hard, you make an effort. You do it, hoping to be successful, which might not always happen.
It might be physical effort:

• She tried to move the cupboard on her own but it was too heavy so she decided to wait for her husband to come home.
• I tried to hear what they were saying in the other room but I only managed to catch a few phrases.
• I tried to open the door but it was locked from the inside.

or mental:

• He tried to understand her but she just cried and cried and never said what the problem was.
• My mother tried to teach me some German when I was little.

 Try + gerund (try doing)

This is when you want to see if it works, as an experiment. You do it, hoping to see what happens. It has nothing to do with the thing being easy or difficult. It is something you do when there is a problem and you are trying to solve it.

• It was really hot last night. I tried opening the window but it didn't help.
• If she doesn't return your calls, why don't you try sending a letter and some flowers?
• I tried adding a little salt, like the cookbook suggested, and it really made the dish taste better!

So you want to achieve something by doing something else. In these examples you want to feel cool by opening the window, he can contact her by sending a letter, I made the dish taste better by adding salt.

Comparison:

He tried to read the newspaper but he couldn't because he had forgotten his glasses. = He wanted to read the newspaper but he didn't see well without the glasses.
He tried reading the newspaper to take his mind off his problems. = He tried to think about something else by reading the newspaper.