Slayer has many roles in the game, it's early game role is mainly trying to get gold coins.
Every time a vampire destroys a building or kills a unit, there is a 20% chance for a small coin and a 5% for a large coin to drop, which gives you respectively 1 and 2 gold and a level. Your slayer is the only unit that can take it, you should try your best and catch these coins early game using your Blink ability, as it is global.
Few tips/notes for catching gold:
Be fast, have a strong map awareness, always keep an eye where the vampires are and if they are chaining other workers, since all players will be trying to catch that gold, you have to be fast!
Gold coins will not drop if your slayer is near the building/unit that is being destroyed, so keep your distance!
Tents are cheap buildings which provide food. Food allows you to increase your population, which means the total number of your workers. Small tents provides 25 food each, so a total of 10 small tents is needed to reach max population (250), or you could upgrade them to big tents, which provides 65 food each, meaning you need 4 of them. Small tents are preffered over big tents, because big tents give 4 gold feed each when destroyed, so 4 big tents = 16 gold, 10 small ones = 10 gold. Tents should be gotten at the start of the game, and must always keep that 250/250, very cheap to rebuild.