How to make a animation play on a player (server sided)?

All you need is a localscript, because animations always replicate and are always server-sided.

Inside the localscript you need to insert an animation object, and input the animation ID in it (which I assume you have).

Then do this script

local player = game.Players.LocalPlayer
local char = player.Character or player.CharacterAdded:Wait()
local hum = char.Humanoid

local animation = hum:LoadAnimation(script.Animation)
animation:Play()

This is a VERY basic script, which plays the animation. You require more scripting if you want to get specific (such as animate only when walking, only when key is held, etc. Since you did not specify, I gave you a base to work out of). Hope this helps.