would like a bodyforce onclick?

Start by getting a reference to the BodyForce Instance that you want to manipulate.

--Examples
bodyForce = workspace.Something.YouBodyForce 
bodyForce = script.Parent.MainBodyForce
bodyForce = Instance.new("BodyForce", script.Parent)
--Etc...

You'll need a boolean value to track whether the force should be enabled or disabled:

switch = false

You'll also need a variable to store the desired force.

desiredForce = bodyForce.force --assuming that you've already set a force

In a LocalScript, get a reference to the Player's Mouse Instance by calling the method GetMouse() on the LocalPlayer:

mouse = game.Players.LocalPlayer:GetMouse()

Then, you'll need to connect a function to either the Button1Down or the Button2Down event:

mouse.Button1Down:connect(function()
    switch = not switch --flip the switch
    if switch then
        --Enabled
        bodyForce.force = desiredForce --set the force to desired for when enabled
    else
        --disabled
        bodyForce.force = 0 --set the force to 0 when disabled
    end
end)

All together:

bodyForce = --path to your BodyForce instance
switch = false
desiredForce - bodyForce.force
mouse = game.Players.LocalPlayer:GetMouse()

mouse.Button1Down:connect(function()
    switch = not switch 
    if switch then
        bodyForce.force = desiredForce
    else
        --disabled
        bodyForce.force = 0
    end
end)

Also, make sure to check out the scripting Tutorials section on the Official ROBLOX Wiki, as well as pages that are related to this question such as PlayerMouse and BodyForce.

You're new to the Scripting Helpers forum (Welcome!) and so I'll give you some advice. In future, try and give more detail to your questions, such as describing specifically what it is that you don't understand, telling us what you've tried so far, adding code that you've tried writing, referencing a tutorial that you read but couldn't understand, etc... this makes it easier to answer your questions, and so you'll be more likely to get a relevant answer sooner.

Make sure you up-vote/approve answers that were helpful to you, as this shows that you respect and appreciate the time that people spend writing them. I hope this helps and if you have any further questions, don't hesitate to ask. (But always try and figure it out on your own first! ;)