To-hit modifers are listed on a chart for easy reference. Shooting can be simplified if you remember that a BS 3 unit hits on 50/50 before modifiers. Just add or subtract as you move up or down from there. Modifiers can get complicated, it is a matter of knowing what your troops can do. The Wood Elf Glade Guard for example has a range of 30, suffers no modifiers for moving and shooting and shoots at str 4 at close range.
The most common modifiers are long range, moving and shooting, skirmished/single mansized model, multishot, hard cover and soft cover. with the exception of hard cover, they are all a modifier of 1, hard cover is 2. Well, these days large target is in there a lot, but it is a plus to your roll instead of a minus.
As an example, a Wood Elf Glade guard shooting at a dragon at long range would hit on a 3+ even if they move and shoot. +1 for large target, no cover, -1 for long range and their BS is 4, they don't have a multishot option. High Elf archers in the same situation would hit on a 4+ if they move because they don't get the Wood Elf ability to move and shoot without modifiers and they are the same BS. Hope it helped.
