Light Scout Drones are the smallest combat drones.
Coming in four variants (with slightly different damage-doing capabilities), Tech 1 Light drones are probably where pilots begin their drone experience due to their low cost and skill requirements. When choosing which drone to fit into your drone bay, keep in mind your purpose for these mini-ships. Ensure you match either their speed or damage-dealing type to your task at hand.
For example, if you intend on killing asteroid belt rats, look at what racial resistances those ships have. Serpentis have low resists to Kinetic damage followed by a slightly higher resistance to Thermal damage. Therefore you should carry Hornet light drones as the 1st choice followed by Hobgobblins as the second choice to be most effective.
Light drones generally weigh in at 5m3 in volume, meaning that any ship that has a drone bay will be able to carry at least 1.
When launched, they orbit your ship waiting for commands. A pilot can attack by locking a target and issuing the command "engage". They then MWD away and do "the business", thereafter returning to orbit their owner's ship.
Like ships, they come with shields, armor and structure. They are, however, relatively weak, and will wither under any sort of determined attack. When deployed, keep a weather eye on the drone tab and see if your drones have attracted aggression (termed 'aggro') which is indicated initially by shield damage. Recall them at that point to force the target to switch 'aggro' to you. After that occurs you may safely redeploy your light drones.
To minimize this, a drone-user may wish to retain his/her drones in the drone bay until NPC foes have locked onto the main ship, then deploy them, and the NPC will stay locked onto the main ship, and let the drone just tear into them. (Watch out for a second NPC wave who may then target the drones, however).
It is most highly recommended that pilots employ familiar keyboard shortcuts to control their drones. Especially the top two commands "Attack" and "Return to drone bay". To have these mapped to rapidly accessable keyboard commands will definitely save you drones and may well aid in saving your ship!
Most PC opponents will have smaller-caliber weapons mounted, which will equally tear into drones. For this reason, in Player versus Player or PvP most pilots employ Warrior drones which are the fastest variant and therefore harder to hit.