Reddit mentions of 100 x 2N2222 NPN TO-92 Plastic-Encapsulate Power Transistors 75V 600mA

Honestly you can get a bunch of the individual stuff separately on amazon. Here are some recommendations I have:

Get a volt meter that can measure ohms and current (mA):

https://www.amazon.com/gp/product/B00KHP6EIK/


Red/Green/Blue LEDs:

https://www.amazon.com/gp/product/B0059H5Z5O/

https://www.amazon.com/gp/product/B004UMA60S/

https://www.amazon.com/gp/product/B0059H5Z5O/


Breadboards:

https://www.amazon.com/gp/product/B01258UZMC/


Jumper wires:

https://www.amazon.com/gp/product/B00ZWEFWO8/


pir (motion) sensors:

https://www.amazon.com/gp/product/B017HP88VI/


transistors:

https://www.amazon.com/gp/product/B00R1M3DA4


resistors:

https://www.amazon.com/gp/product/B0185FGTSS/

https://www.amazon.com/gp/product/B0185FGN98/


The multimeter is great, you can make sure you wont fry your GPIO outputs. Try not to pull over 16mA of current per pin to avoid damage. Use a 1k or 330 ohm resister accordingly. You can also do a lot of cool stuff with a transistors and LEDs.


I've been documenting a lot of the electronics stuff I've been teaching myself; About six months ago I was where you were, setting out trying to learn how to use all these components. Feel free to reach out if you have any questions. I'd recommend going to the oldest post on my blog and reading in order if you want some ideas: https://supertechnologyknowledgequest.blogspot.com

PM me with any questions, I'd be happy to point you in the right direction for anything you are trying to do for which I can help! Best of luck!

edit: the multimeter is no longer on amazon, just find one that lets you read resistance AND current (milliamps).

I have done something very similar to this, as I have worked on projects where I needed to control common-anode RGB LED strips. You should just need a common NPN Transistor. Here is a link to some I found on amazon that I find tend to work well, and the bulk pack is pretty nce, And Here is the datasheet for those specific transistors.

If all you want to do is be able to turn the LED on and off, the circuit should be fairly simple. Connect VCC (12v) through a current-limiting resistor to the anode (+) of the LED. Then connect the cathode (-) of the LED to the collector of the transistor, (can be seen in the diagram/datasheet) then connect the emitter of the transistor the ground (- of the power source). And connect the output pin from the Arduino through a small-value resistor to the base of the transistor. With that, you should be able to use the Arduino output to control the higher-voltage LED with digitalWrite(pin,HIGH) turning it on, and digitalWrite(pin,LOW) turning it off.

Here is an example of what that would look like. Ignoring however you plan on powering the Arduino itself, you can see how the LED, transistor and output pins are connected.

 

NPN Transistors normally have 2 "modes" per se. They have an analog mode which uses a change in normally very low voltage to change how much "on" they are, meaning they let different amounts of current flow from the collector to the emitter (In this case the voltage path of the LED) depending on how much current is flowing from the base to the emitter (Arduino to ground, as when the output goes high, it allows current to flow through the transistor's base to the emitter). However in this case, the transistor is mostly going to be functioning in the saturation region, meaning that the Arduino is likely going to be putting out enough current that the transistor will either be completely ON or completely OFF, and you wont get much analog function out of it. However if you want to be able to dim your LED, you can use PWM to very quickly turn it on and off, which can give it the effect of dimming it.

 

TLDR: Use a transistor. Likely NPN would work well.

Edit: In the circuit schematic tool I used, they had the ATMega, but not an Arduino itself. Treat the mega shown as if it were an Arduino, Ex. Has voltage regulators, input pull-ups, etc. The VCC is the arduino's RAW or Vin

I got a 100 pack of 2N2222 NPN transistors from Amazon for $4.60. Here's the link.