21a) Terms are "like" if they contain the same constellation of variables, x² in this case. The terms like 3x² are 3x², -x².
21b) Terms in the list that have x as the variable (like -11x) are -5x, 4x, 11x.
22a) We're unfamiliar with the meaning of the instruction to "draw the tiles". You will need to do that on your own. The x-terms can be combined, and the constant terms can be combined. The simplified expression is
... 5x - 3x + 2 - 4 = 2x - 2
22b) 2x² + 4x + 2 +3x² - 2x - 3 = x²(2+3) +x(4-2) +(2-3) = 5x² +2x -1
23a) 6x -x +2 -6 = x(6-1) +(2-6) = 5x -4
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Combining like terms is an application of the distributive property. You can factor the variable(s) from like terms so that what you have left are the coefficients. Then you add those. This is illustrated in the answers above to 22b and 23a.