How to use this volt tester?

[tomb]

Hello!

I am trying to debug a Li Vibe pcb I purchased and populated.  Most complex build so far, so unsurprisingly, it has not worked first time.

I bought a volt tester (attached image) from a DIY store here - I don't really have access to anything else/better, living where I do. 

I have done some google research, but I cannot for the life of me work out how to use it/find a tutorial with a volt tester with a clip like this one.

I have tried attaching the clip to the 9v in, and poking around the circuit - the LED sometimes lit up, sometimes not.  Similarly, when attaching the clip to the ground.  I'm wary of just jumping in incase I damage components, however.  Any pointers for how to properly follow the schematic along and find where the issue is are greatly appreciated!

Thank you!

[somnif]

That's not really the wort of tester we use in our circuits, its mostly a "Is there voltage here or not" thing. They used to be made with neon tubes and were used to detect wall socket "mains" voltage. You'd clip it to ground, then poke around. If it lit up, that meant it wasn't safe to work. Just a bare simple safety measure, voltage or not.

For circuit work you want a digital multimeter (aka DMM). You can pick them up for quite cheap online, though I don't know what shipping would be like to your part of the world.

[tomb]

Thank you!  Your direction is appreciated