You want to get started with Jekyll on MacOS ? Here is what you can do
Configuration:
MacOS: Sierra 10.12
Jekyll: 3.7.2

1. Go to the offical website

You should see this:

Before you do all this, you will probably need to install Ruby, in order to use gem

2. Make sure gem is available

Open a terminal and Type gem -v

It should prompt some numbers, like 2.7.4
If not, you need to make gem command available from everywhere in you mac, click here to know how in 1 minute

3. Make sure jekyll is not already installed

Type jekyll -v

It should say:
-bash: jekyll: command not found

4. Install jekyll

sudo gem install jekyll bundler
Type your password when prompted

5. create your first jekyll website called ‘exampleWebsite’

Type jekyll new exampleWebsite

6. Run and browse ‘exampleWebsite’

Type cd exampleWebsite
Then type bundle exec jekyll serve

Open a browser (Chrome for instance) and go to url http://127.0.0.1:4000/

that’s it !

7. Further reading

I recommend the official doc, and also some videos like this Youtube Tutorial

TroubleShooting

If you see something like:

Bundler could not find compatible versions for gem "bundler":
  In Gemfile:
    bundler (~> 1.12)

  Current Bundler version:
    bundler (2.0.1)
This Gemfile requires a different version of Bundler.
Perhaps you need to update Bundler by running `gem install bundler`?

It is probably because you have installed bundler globally as well as locally.

Solution: try to remove one of them by typing gem uninstall bundler and try again. More info here