I'm a refugee from another country but has a passport and invitation letter to come to the united states how can i get a visa

You would apply for a visitors visa under the same rules as any other visitor to the United States. It would be up to the American consular officer as to whether you have proved that you have non-immigrant intent. Items that you can show to prove nonimmigrant intent are your ties and bonds with Germany including job, bank accounts, ownership of property, etc. The invitation letter will of course also be taken into account. Due to the limitations of the Lawyers.com Forums, Alan Lee, Esq.'s (the "Firm") participation in responding to questions posted herein does not constitute legal advice, nor legal representation of the person or entity posting a question. No Attorney/Client relationship is or shall be construed to be created hereby. The information provided herein by the Firm is general, and requires that the poster obtain specific legal advice from an attorney. The poster shall not rely upon the information provided herein as legal advice nor as the basis for making any decisions of legal consequence.