I need to know how to find q1 q2 and q3, when the info is in a table eg 10<t<25 frequency is 3 that sort?

sorry for the brief question< i need to know how to find q1 q2 and q3 for plotting graphs and box plots but i get muddled up with like when to use frequency density,mean and how to actually find q1 q2 and q3, can anyone just summaries to help me or give me some examples thanks *)