AK-47 rifles were designed to be maintained in the field with few or no tools. Installing a trigger is pretty simple and straightforward, with a few considerations.
The trigger used in the photos is an ALG Defense AKT trigger. It is an excellent trigger and similar to most in terms of installation. Some other aftermarket triggers are different, but this should cover most.
Every AK receiver is different even if it came from the same country of origin. Some are completely different, so make sure the trigger you purchase is designed to be used in your rifle — never assume they are “all the same.” AK parts are seldom the same, so minor fitting might be required.
Another thing to be aware of is that in many cases, the safety fit to your existing trigger might not work with a new one. You might have to file the locking notch so it makes proper contact with the trigger bar. It is supposed to allow it to move when down and prevent it from moving when up.
AK triggers come in single- and double-hook. Most receivers will accept a single-hook trigger. Double-hook triggers might require you to file out room for the second hook. If this is the case, it might be time to take it to a gunsmith. It is not difficult, but you are filing on your receiver. Single-hook triggers will work just fine in a double-hook receiver. You might have to complete some minor fitting to make sure the trigger moves through its entire range of motion without hanging up.
Make sure you have a clean area to work and the instructions, as well as some patience. Once completed, you will enjoy shooting your AK that much more and you will have a better understanding of its operation.