What does Linux chmod +755 and chmod +777 mean?

You can enter ls-al on the Linux terminal, you can see such as:
   -rwx-r--r--(altogether 10 parameters)
The first one has nothing to do with chmod, regardless of the parameters.
2-4 parameter: belongs to user
5-7 parameter: belongs to group
8-10 parameter: belongs to others
And then it's simple.:r==> readable w==> writable x==> executable
               r=4      w=2      x=1
So 755 stands for rwxr-xr-x.
Do you understand me?

755 on behalf of the user to the file has read, write, execute permissions, the same group other people have the ability to execute and read, no write permission, the other user's permissions and the same group of people permissions ...

777 stands for, User,group, others, both read and write and execute permissions.

What does Linux chmod +755 and chmod +777 mean?