SHOULD AND HOW DO I GET FOREIGN PATENTS?
Whether you should get foreign patents is a business decision.
Your US patent only protects against infringement in the US. Therefore, products that are being imported into the US, sold in the US, or offered for sale in the US can be stopped by your US patent.
Likewise, foreign patents are generally country specific. If you obtain a patent in China, that patent can only be used for infringement in China. Some foreign patents, however, can cover multiple countries - like a European patent. An EU patent can cover countries that are part of the European Union.
If your business is exclusively conducted in the US, then it may make little business sense to seek patent protection outside of the US.
On the other hand, if you manufacture outside of the US, it can make business sense to obtain patent(s) in the country(s) where you manufacture.
As another example, if you sell your product in foreign countries, then you may want patents in those foreign countries. However, if your sales in any one foreign country is minimal, then it may not make financial sense to seek a foreign patent.
How you obtain a foreign patent can be done in a couple of ways.
Within one year of filing your US patent application, you can file your US application directly in a foreign country. Doing so will give you a "priority" date for your foreign application that goes back to your filing date of your US application. (You generally want to always have the earliest filing date that is possible.)
Alternatively, within one year of your US patent application filing, you can file a PCT (Patent Cooperation Treaty) application. This can be useful if you want to file in several foreign countries. Your PCT application will undergo some initial review, and then you can use the PCT application to enter individual countries for patents.