which stations to use

I am arriving at Bejiing airport at 0855hrs on 21st April, travelling onwards to Tangla hotel in Tiajiin, and looking for best advice on which stations are closest and how best to go about booking trains. Should I book before I leave home or is it ok to purchase once I get there. What time window should I give for all the travelling between landing and getting to railway stations and then best way to travel once in Tiajiin X. Many thanks from a female travelling alone x