Welcome. Not in English, but i can get you one in French
Seriously, they are very graphic and intuitive. Regarding the Spanish one, the main commands are the zoom (bottom right) the meteo (top right - on -off and then you have to choose the time: 6-12-18 or 24 h) and the cursor on the bottom on the middle. On that one you can pull the red arrow back and then, on the left click on the arrow and you can see the boats retracing the courses. You can adjust the speed on the left also.
On the French one, the meteo (weather) is less visible but I find the classification, on the left bar more agreeable.
Jean le Cam - Président • Barcelona World Race 2011
The distances are measured in nautical miles.
The distances between the boats take into consideration the distance but also the wind forecast. For example, a boat can be nearer the final in distance but if it has ahead one or two days with weak winds can be behind another boat, that is further back (in distance) but has ahead one or two days with strong winds. I hope this confusing explanation makes some sense
Anyway, most of the fun of following the race is to try to find the better course to take advantage of the wind. The better course is almost never the shorter. Things become more interesting when there are several options.
For example, if you have a look at the forecast at 12-18-24 hours you are going to see that there are a big hole without wind around the Canary Islands. That's why they are all going west, to get stronger winds and avoid the anti-cyclone. But than there will be some that will prefer to go more west to get more wind and others that will prefer less wind and a shorter distance, or to try a passage nearer the coast of Africa where in 24 hours the wind will be more steady.
That's the game and also a way to learn how to navigate at a "decent" scale