Need help modding server

I’m just making a small server for me and my friends to play games on. I do have a hosting company, The Minecraft Hosting, and I have a few options for servers. Spigot, craftbukkit, vanilla, and mod. Mod says “Upload your custom jar and upload name it: custom.jar”, but I don’t know what that means.

Minecraft VPS Hosting via Need help modding server.


at net.minecraft.server.v1_8_R3.DedicatedServer.aO(DedicatedServer.java:412)

v1_8_R3.DedicatedServer.aO(DedicatedServer.java:412) [spigot.jar:git-Spigot-db6de12-18fbb24]. at net.minecraft.server.v1_8_R3.DedicatedServer.B(DedicatedServer.java:375) [spigot.jar:git-Spigot-db6de12-18fbb24]. at net.minecraft.server.v1_8_R3.MinecraftServer.A(MinecraftServer.java:654) …

Minecraft VPS Hosting via at net.minecraft.server.v1_8_R3.DedicatedServer.aO(DedicatedServer.java:412).