True. At a real basic level, aircraft navigate along designated routes called airways between navigation beacons (VOR = VHF Omnidirectional Range beacons or NDB = Non-Directional Beacons). There are low altitude airways used below 18,000 feet - these are designated with the letter "V" on charts followed by a number - that "connect" beacons. There are high altitude airways or jet routes which have the letter "J" followed by a number on high altitude charts which also run between beacons. VORs and NDBs are named and have their own designations on charts.

For example, a United flight from Sacramento to Denver might file a flight plan to use the DUDES9 departure procedure (which defines HOW to properly leave Sacramento International Airport on an easterly route), fly to the Mina VOR beacon in Nevada, then follow the J84 high altitude jetway to the Meeker VOR beacon in Colorado, then use the TOMSN4 (Thompson-4) arrival procedure which governs arrivals from Meeker into Denver International Airport.

Occasionally flight crews will try to get more direct routing with a request to Air Traffic Control. For example flying from Chicago or Denver back to Sacramento flight crews might ask, enroute, for "direct to Squaw Valley", which is the VOR near north Lake Tahoe and the starting point for descents into Sacramento. If they are granted "direct Squaw Valley" from ATC (which depends on weather, traffic, and whether or not the military restricted airspace which takes up a big chunk of central Nevada is in use or not), then the trip goes a bit faster because it's more of a straight line.

I'm not a pilot; learned all the above listening to ATC on United's channel 9 over the years and hanging around Flyertalk.