Me comment in the details if you have any questions and answers in the answers you

Relations are functions if every input has exactly one output

So, the first on is a function because each x value has one y value. Meaning, for example, (3,2), 3 is the x value, which is the input, and 2 is the y value which is the output. But within that set of relations, 3 only has one output which is 2.

The second one is not a function because 2 has 2 outputs. (2,3) and (2,5). 2 has an output of 3 and 5. Every input can only have one output. So this isn't a function

The third one isn't a function because 6 has two outputs. (6,3) and (6,6). 6 has two outputs of 3 and 6, so it's not a function

The last one isn't a function either because 6 has two outputs. (6,8) and (6,4). 6 has the outputs of 8 and 4. So, it is not a function

Hope that helps :)