1. On your page's post click "Boost Post" on the bottom right corner of the post.
2. The pop up box will come up which allows you to set up how exactly how you're going to be boosting your post.
3. Set your audience to be either just people who like your page, people who like your page and their friends, or choose target to specific people you want. You can specify target people with certain interests in specific locations that you want the post to be seen by.
4. Set your budget. Facebook will estimate you how much reach you will be getting by paying X amount of money in X amount of time.
5. Choose how long you want your post to be running by. The longer the duration is, the less the post will be promoted in one day. Facebook will tell you estimates number of how much reaches the post will have in total.
6. Paying for your boosted post with your credit card. Enter your credit card information here.
7. Hit the "Boost" button. Waiting until the post gets approved and you are all set!