Help making a script that starts an animation when you press a key?

Alright, the other answer was a little more complex then it needs to be.

First put the animation in a script. Then make the scripts code this:

game.Players.PlayerAdded:connect(function(player)
local anim = player.Character.Humanoid:LoadAnimation(script.AnimName)

local mouse = player:GetMouse()

mouse.KeyDown:connect(function(key)
local correctKey = "e" -- make whatever key you want
if key == correctKey then
anim:Play()
end
end)
end)

Now, if you wanted to do a key that wasn't a letter then you'd need to find the key's number and then use this code:

if string.byte(key) == correctKey then 

Opposed to:

if key == correctKey then 

Try something like this?

local player = game.Players.LocalPlayer
local humanoid = player.Character:WaitForChild("Humanoid") -- Wait for the Humanoid to exist
local animation = Instance.new("Animation")
animation.AnimationId = "http://www.roblox.com/Asset?ID=ASSETID" -- Replace ASSETID with the id of your animation
local animTrack = Humanoid:LoadAnimation(animation)

game:GetService("UserInputService").InputBegan:connect(function(inputObject)
    local keycode = 0 -- Replace 0 with the keycode of your key

    if inputObject.KeyCode == keycode then
        animTrack:Play()
    end
end)

Find a list of keycodes on the wiki: http://wiki.roblox.com/index.php?title=API:Enum/KeyCode

You may have figured it out but this may be the best answer.

This is what I used: * UserInputService * Local Script

local uis = game:GetService("UserInputService")
local plyr = game:GetService("Players").LocalPlayer
local anim = Instance.new("Animation")
anim.AnimationId = "rbxasset://" --Animation id here

uis.InputBegan:connect(function(key, thing)
    local char = plyr:WaitForChild("Character")
    if key.KeyCode == Enum.KeyCode.A and thing then --Could be any letter(capitalized), Space, Escape, etc.
        local h = char:WaitForChild("Humanoid")
        h:LoadAnimation(anim):Play() --Custom animations run for 2 seconds(as of 2015)
    end
end)

Hope it helps!

Enum works a little different from the string.byte(). If you go here you can see in the first line, there is the key, the second there is the Value and the end is the description(which isn't added yet). So from this chart, 0 is actually the "Unknown" key.