Sometimes my students get confused when using these two words. The difference is quite simple: “travel” is mostly used as a verb, whereas “trip” is a noun. Thus, you can say:
“I will travel to Croatia this summer.” “ I will go on a trip to Croatia this summer.”
“Travel” can also be used as an uncountable noun meaning “travelling in general”:
“People say travel broadens the mind”
“Air travel is much cheaper these days”
The plural “travels” means a long trip in which several places are visited, as in “Gulliver's Travels”, the book by Jonathan Swift in which the doctor Lemuel Gulliver embarks on several voyages that take him to faraway, exotic lands with even more exotic dwellers: Lilliput, the land of tiny people, Brobdingnag, the land of gigantic people, etc.
Another related word is “journey”, which means the movement to and from a place, whereas “trip” also implies a visit to the place you've gone to.
“I hope you have a safe journey”
“I really enjoyed my trip to Rome last year”.
Depending on the means of transport, different words can be used instead of “journey”:
Voyage (pronounced/'vɔɪɪdʒ/) is a long journey on a ship or boat. “The Titanic sank on its maiden voyage”
“Crossing” is a short journey in a boat or ship. “The ferry crossing to Ceuta took fifty minutes”.
“Flight” is a journey in a plane. “Our flight was delayed due to air controllers' strike”
“Drive” is a journey in a car. “Madrid is a five hour drive from Malaga”.
“Ride” is a short journey by car, bike, horse. “Let's go for a ride in my new car”
Now you can do this exercise to see how much you have learnt: