Sundar,
Because I do not know where your understanfing is breaking down, I'm going to start at the beginning.
1) USING MATH LANGUAGE PROPERLY:
Make sure you understand the meaning of the symbols you see on the page. It helps to write the equations out in proper math language...

Math didn't always use symbols--when it was first imported from Arabs, algebraic "sentences" were written out in words. For example, instead of "x," the phrase "the unknown thing" was used. Try writing your math notes in plain Elnglish for a day, and you
may understand...

Subtraction can always be thought of as adding a negative number.
For example, 1 - 1 is the same as 1+ -1.
I love that your calculator shows this! It looks weird at first, but if you get used to thinking...