I am only familiar with US topos, but a point the other answers miss is that the US Geological Survey have mapping standards, and most non-USGS maps (at least in America) match the USGS standards.
I'd suggest you start by learning the standard symbols in your area. Make up flash cards and you can easily quiz yourself as you have a few minutes (this is a great way to pass time while on the bus/train to work).
As for being able to navigate, topos often have more information than is necessary to walk through the woods and come out alive. For example, there are 3 symbols for a mountain top. The only difference is the precision of the measured altitude. There are 2 symbols for mines (vertical/horizontal). The brown elevation lines mark hills and valleys one way, but a depression another way (a circular pattern with lines pointing to the bottom of the depression).
I was taught orienteering by a few folks, and the fancy ways didn't really work for me, but finally I met an old, grizzled marine and his method was dirt simple, and works for me:
- Keep the map in your hand at all times. If you can't look at the map, you are much more likely to lose your place on it, or "find" your place on it in the wrong hill/clearing/etc.
- Fold the map so it is a square that fits comfortably in your hand. Yes, this means that if you go to an area frequently, you will need to replace a worn out map, but it's better than the alternative.
- Keep the map in a plastic bag to keep the paper dry, unless you are refolding the map, or looking at tomorrow's hike while under a tarp.
- Hold the map so that you are walking from the bottom to the top. Turn your body left? Turn the map too. The map should turn the opposite direction you are turning.
- If you are in a boring area of trail (for example, in the middle of a forested part and there's nothing but "green tunnel" around you, figure out what the next feature of the walk is. Are you going around a curve? Coming into a clearing? Crossing a creek? Figure out what the map says you will do next, and look for it.
- If you are walking on a trail marked with blazes, also look for the blazes. In the US National parks, there is the convention that if you stand next to a blazed tree on the trail, you should be able to see the next blaze or 2*.
- Try to keep your thumb where you think you are.
*Yes, sometimes this does not work out because the tree the next blaze is on has fallen due to weather/disease/forest thinning, etc. But works 95+ percent of the time.