I am learning about SPSS, and I have some questions:

1/ In Chi-square tests, there are terms "Pearson Chi-Square", "Likelihood Ratio", "Linear-by-Linear Association" and "N of Valid Cases". Could you please tell me what do they represent? Moreover, why the Value of Pearson Chi-Square is 6.000a, what does this mean?

For example
Chi-square tests
Value df Asymp. Sig. (2-sided)
Pearson Chi-Square 6.000a 2 .050
Likelihood Ratio 8.318 2 .016
Linear-by-Linear Association 5.170 1 .023
N of Valid Cases 10

a.6 cells (100%) have expected count less than 5. The minimum expected count is 1.50.

2/ In this case, the significance level is .05, so how to define the difference between the expected and actual counts?
3/ In ANOVA and Post-Hoc Tests, what do "Sum of Square", "Degree of Freedom", "Mean Square" and "subset for alpha" represent?

You do not need to be worried, these are not SPSS-specific concepts
but statistical concepts. So the information you can get by reading
introductory books and websites about Chi square statistics and
ANOVA statistics also applies here.