For iOS 12 — 12.1.2 A12 Devices:
Say hello to https://chimera.sh/

Can an I run all tweaks?
No. Check this Google Document to see If you can run it. https://docs.google.com/spreadsheets/d/1SJ-BKj9avEz5ESQOGLNEKsNeAptboWskAJrKaTXtnh8/htmlview
I missed the boat for iOS 12.
Say Hello to: Electra. For iOS 11.0 – 11.4.1.

I’m New To jailbreaking how can i tell if i can?
Step One: Check your firmware.
Open the “Settings” app on your iPhone, iPad or Apple TV.
Settings < General < About . Look For Version: Like bellow.

How to Install Jailbreak On Device?
Great Question. How we have two options. One is “Self Signing” the app to your phone similar to how you would test an app you are developing. Which isn’t as hard as it sounds. Using an easy tool called “Cydia Impactor”.
The alternative is using a signing service. Like https://ignition.fun/ . I don’t however recommend this option so i will only cover self-sign.
Cydia Impactor:

(WIN|MAC|LINUX 32/64 bit)
Download Cydia Impactor to your current os and install. Once installed open it and prepare your “IPA” file for either chimera or electra.
Note: Before installing jailbreak add a beta profile to avoid updating to newest iOS Version. Go to betaprofiles.com to download tvOS 12 profile.
Once beta profile is installed simply drag your electra IPA or Chimera IPA file into the Cydia Impactor Window.
Once beta profile is installed simply drag your electra IPA or Chimera IPA file into the Cydia Impactor Window.

Once Installed go over to Settings < General < Profiles and verify Electra Or Chimera. Then Simply open the newly installed Chimera.app or Electra.app and hit jailbreak. Be sure your device is in airplane mode. When Running the app.
Thats pretty much it.
Install ReProvision to avoid having to resign every 7 days. By adding repo.incendo.ws source to Sileo your new package manager. And Installing ReProvision.
If you Run into bugs when installing tweaks. Remember it’s the tweak not the jailbreak. Most Tweaks have contact info to developers.
Hope this guide was helpful if not. Let me know i’ll update this.