Confusion with how to ground base of transistor
Now that you've added your schematic, I can immediately see a number of problems with it.
Firstly, you must have a current-limiting resistor on the base of your transistor, or your transistor will go up in smoke.
Secondly, there's no reason here to use an npn transistor for high-side switching; you should put it on the low side.
Thirdly, you've got your LED connected backwards. It's not going to light, and might be fried if you hook it up to power.
I'm assuming your LED strip has current limiting resistors built in, so leaving that off the LED is presumably fine.
Here's a corrected schematic for it:



simulate this circuit &ndash; Schematic created using CircuitLab
I didn't bother to work out what value resistor you should use, because I don't know how much current your LED strip needs. Be aware that the BC377 can't handle more than 0.8 amps though.