Zombies are one of the easiest mobs to kill and defend yourself against in minecraft. They closely resemble the default player skin, though, of course, dead and rotten.
When killed, a zombie will drop 0-2 pieces of rotten flesh and 5 experience points. There’s also a rare chance they drop either an iron ingot, iron helmet, iron shovel or iron sword. Note that rare drops will only drop if the player kills the zombie.
Their drops make them one of the more useless mobs in minecraft. Even though rotten flesh can be eaten, there’s an 80% chance it gives you food poisoning, which will drain your food bar by about 2. However, eating large amounts of rotten flesh will still only drain your food bar by 2, if you get food poisoning. It’s also possible to cure yourself by drinking milk.
Zombies can be found anywhere in the Overworld, though they require a light level of 7 or less to spawn. Zombies will catch fire in direct sunlight, but they’ll look for shade or water during the day. This allows them to survive throughout the day but renders them pretty much immobile. Rain will protect them as well, allowing them to move around freely and attack you during the day.
Zombies can also be found in some dungeons with skeleton spawners. Zombies make loud grunting noises which makes them very easy to detect, even through walls.
Like most mobs, zombies have a line of sight that extends up to 16 blocks. If a player comes within their line of sight, the zombie will start to chase the player, though they’re quite slow. Zombies attack by touching the player, which sort of mimics a biting attack. This makes it very easy to attack them without being able to be attacked back. The knock back effect of swords is sufficient to keep them away from you.
Dispite looking like brainless monsters, zombies have a good AI which allows them to overcome most obstacles, including high drops, lava pools, fires and maze-like obstacles. They can also climb ladders and vines, but will only do so if they’re directly between the player and the zombie.
Zombies can and will destroy wooden doors, but can only do so on hard difficulty and in hardcore mode. Iron doors, trapdoors and wooden fences cannot be broken.
If confronted with a large amount of zombies, there are pretty much 4 things you can do.
You can either fight. By hitting the zombies one at a time you’ll be able to keep them all away from you. If there are still too many coming too close, walking backwards often helps.
Run. Zombies are very slow, by running 17 blocks away from them, the zombies will lose interest and stop following.
Block them. This isn’t always a possible solution, but often works in caves. Block their path but leave a hole through which you can attack, without being attacked by them.
Use splash potions of healing. Splash potions of healing will damage the zombies, all of them, while it will heal you. This works great in dungeons with zombie spawners. Splash potions of harming will heal zombies.
Keeping zombies out of your base is very easy. Lighting up your base and its surroundings is often enough to prevent them from spawning and to prevent any zombies outside the light areas to wander far enough into your base. If you want to be completely safe, fences will work perfectly. The zombies cannot jump over them, though you can still attack them, with either a sword or bow. Note that skeletons will be able to shoot you and spiders can climb over the fence.
A moat or wall is your best option though, especially if you fill the moat with lava. Nothing will be able to pass it.
Raids happen randomly at night in villages. A mob of zombies will spawn and they’ll try to break down the doors and kill the villagers. Their only defence are iron golems roaming the village, which will automatically engage any hostility.