Is anyone here willing to teach me about string manipulations?

I just started scripting on ROBLOX last month which makes me a beginner, Is anyone willing to teach me the basic functions of string manipulations

Here are a few that i know

STRING.BYTE

local str = "Hey, whats up"

string.byte(str)

STRING.DUMP

local str = "Hey, what's up"

function func()
    print("Hello how are you")
end

s = string.dump(func)
print(s)

STRING.FIND

local str = "Hey, like LUA?"

print(string.find(str,"LUA"))

Can you teach me the basics, and more strings? Would be appreciated : -)