Basically, if you have 2 telescopes with diameter of 1m and 10m baseline(distance) between them, when you synchronize them and observe the same object - they act as a one telescope of 10m. Nowadays we are putting lots of telescopes on larger and larger distances (VLBI = Very Large Baseline Interferometer).
The one bellow is a classic one, you can also check out this visdeo for a little intro of this interferometry! :)
