Main Merchant is online

Have not heard of the merchant navy before and am curious at how different it would be (if at all) to what i would be doing in the merchant marines. For example would i travel more in the merchant navy and what type of jobs do they offer over merchant marines. Lastly could i join the merchant navy after already getting my credentials for the MM or would i have to get additional training and paperwork before i could join. And if anyone can give me a number for any US based merchant navy office i would like to check it out.

I want to open up a website to sell stuff, but I’m not sure if I should use a Merchant account or a Paypal account? What’s the difference?

I’m a new’be in web and I pretend to setup my online store. The question I have is … What is the difference between a merchant account and a payment gateway? and why do a merchant would require any of those services?