There is not one standard way of writing a transcript, so you will have to look at the example you were given. However, general rules are:
Each speaker has a new line. They are identified each time they speak, a bit like a drama script.
Pauses are indicated by square brackets with the number inside indicating the length in seconds. E.g. I was er [2] wondering if I could go. For a pause of less than a second use square brackets and a full stop [.]
When there is overlap (two speakers talking at the same time, such as when someone gets interrupted) write the second speaker's words below the part where they overlap, and place both in brackets. E.g.
Fred: Can you tel me the [time]
John: [half p]ast eight
For non-lexical items, such as laughter, use square brackets again [coughs]
Write down exactly what you hear, not what you remember. There will be some repetition and false starts. I needed to [.] I needed to [2] I just wanted to get away