save up for something/ to do something = save money to buy something (e.g. Bob is saving up for a trip round the world)
see somebody off means go with them to the airport/ station to say goodbye (e.g. Bod was going away. We went to the station with her to see her off)
send something back means return (e.g. My letter got sent back to me because I used the wrong stamp.)
set off means start a journey (e.g. We set off very early to avoid the traffic. (= we left early))
set somebody up means trick, trap (e.g. The police set up the car thief by using a hidden camera.)
set up an organisation, a company, a business, a system, a website etc. means start it (e.g. The government has set up a committee to investigate the problem)