"to have composure" means to act calm and professional in a situation. "to be held accountable" usually means that a set someone will be blamed if a problem happens and has to explain why the problem happened when it does. This seems a little odd to be written on a resume actually, a similar but more common expression for a resume would be "I was/am responsible for...".

“Composure” means self control, calmness. Example, “In the difficult times she had a lot of composure. “. “Being accountable ” means being ready to explain your actions, being responsible in some way . Example, “By being an accountable leader he grew his organization to the highest level.”. :)

Composure is being in control of oneself. So, if a basketball player says, "I lost my composure on the court," it might mean that they stopped being calm and in control of their emotions. If they kept their composure, it means they stayed calm. Accountable means having to justify one's actions. So, on a resume, accountable might mean that they had a job which other people ensured they were doing properly, and that person proved themself up to the task. Hope that helps you.