Pull factors are positive factors that attracts migrants to go to the certain destination. For example you may consider going abroad because of higher standards of living, lower costs, better healthcare, better job prospects, beautiful scenery and many other factors that you find attractive in a certain place.
Push factors are negative factors that force you and make you want to leave your place of origin. Those factors include low standards of living, high unemployment rate, riots, war, unstable economy and many more.
Push and pull factors might be the opposite of each other. For example ‘job prospects’ might be bad in your place of origin (which means that getting a job in your place of origin might be hard), which is a push factor, but at the same time it might be a pull factor in your destination, when the job prospects are really good, so you can expect to have a job over there.