Conditional probability and entropy: How do I interpret given data?

As the title explains, I never could understand probabilities. It's one of those things that how much I try, I can't quite understand.

I have to do one homework exercise about entropy and I'm given a set of probabilities. I know how to calculate entropy but I don't know how to interpret the given data.

The alphabet is S={1,2} and the conditional probabilities are P(1|1)=0.8 P(2|1)=0.2 P(1|2)=0.6 P(2|2)=0.4 and P(1,2)=P(2,1)I've created this table (don't know if it is right or not):

| X = 1 | X = 2

Y = 1 | 0,8 | 0,2

Y = 2 | 0,6 | 0,4

I know that I need the probability of 1 and 2 to calculate the entropy. To get the probability of 1 is like this?

P(1)=P(1,2)P(2|1)

If so, How can I get P(1,2)?

I know that P(1)=0.75 and P(2)=0.25 but I don't understand how to get to this result

As the title explains, I never could understand probabilities. It's one of those things that how much I try, I can't quite understand.

I have to do one homework exercise about entropy and I'm given a set of probabilities. I know how to calculate entropy but I don't know how to interpret the given data.

The alphabet is S={1,2} and the conditional probabilities are P(1|1)=0.8 P(2|1)=0.2 P(1|2)=0.6 P(2|2)=0.4 and P(1,2)=P(2,1)I've created this table (don't know if it is right or not):

| X = 1 | X = 2

Y = 1 | 0,8 | 0,2

Y = 2 | 0,6 | 0,4

I know that I need the probability of 1 and 2 to calculate the entropy. To get the probability of 1 is like this?

P(1)=P(1,2)P(2|1)

If so, How can I get P(1,2)?

I know that P(1)=0.75 and P(2)=0.25 but I don't understand how to get to this result