When you try to do something, you make an effort to do it. It may be difficult, so you may have to expend energy in the attempt to do it. When you try to do something, you may succeed, or you may fail.
I tried to lift the heavy box.
I tried to find my lost keys.
I tried to see over the fence by standing on tiptoe.
I tried to touch the ceiling by jumping as high as I could.
I tried to open the package without tearing the beautiful gift wrap.
When you try doing something, you do it with the intention of finding out what will happen when you do it. When you try doing something, you succeed. Your purpose was not to see if you would succeed or fail, but to see if your doing it advanced your cause, helped you to make some progress, or solved your problem. When you try doing something, you are trying to solve a problem.
The door was stuck shut, so I tried shaking the doorknob (to see if that would open it).
The door was still stuck shut, so I tried hitting it with a hammer (to see if that would open it).
The door was still stuck shut, so I tried prying it open with a crowbar (to see if that would open it).
so as you see there are 2 ways to use a verb after try , with 'to' or with 'ing'
and we don't have '' try understand'