I'm assuming you mean the Skulltulas?
You can listen for them. They're relatively loud compared to the rest of the audio, if you're in the right area when the web shows up. If it's really loud and you don't see it, it may be on the other side of a wall, or under a rock that you need to bomb before you attack it.
To control the map, you can switch between characters (when the mission allows it), as well as use the Start menu to command characters to stay in certain places, go after certain enemies, stay with a certain other character, etc. You can tap their face, tap a place on the map, and if there are mobs/objectives there, you can select one from the list and the character will focus on that.
For solo maps, I tend to slowly take over these, unless there's a very urgent objective to take care of. The most pressing ones tend to be going after stronger monsters that can go after and mess up your keeps. Take over as much as you can while activating the Owl statues whenever you can. If you feel like getting the hidden chests, the Skulltula, and the objectives all at once are a bit much, focus on the main mission first, and familiarize yourself with both the map and the objective, then go back to find everything you need that you didn't find on the first run.
If you're having trouble because you need a certain character to find a certain chest or do a certain mission, you can give up Rupees to level characters up, with the level limit being whoever is currently your highest character.
I also recommend checking the Badges for each character often, since you unlock new combos that way, and stuff that makes it easier to clear objectives, such as depleting the weakness gauge faster, taking over a keep more quickly, getting better potions, etc.