Welcome to SaleHoo :
Being new I would suggest going through our New User Manual which you can find in our Link hidden: Login to view section, simply scroll down the to the 6th one.
Another really helpful group of information is this forum thread on What to ask dropshippers - Link hidden: Login to view
How do you contact dropshippers or other suppliers for that matter starts with you doing your research. Research the type of products you are going to sell and search for suitable suppliers to use. You make use of our Research Labs to help you find profitable niches and our directory to help you locate the right suppliers.
Once you have narrowed down y our search then its time to contact your suppliers by either sending them an email or by calling them.
Hope this helps!