Lord Sathyanarayana is another form of Vishnu (the creator). Pournami puja is usually done on the days of pournima and ekadasi of every month. It is auspicious to worship the lord during these days. As  per puranas lord Vishnu himself suggested sage Narada to perform this puja for the benefit of mankind in skandapuranam.

Who should do this Puja: Head of the Family who are looking for continued prosperity of the family and for removing any obstacles in the process

मङ्गलम्भगवानविष्णुः, मङ्गलम्गरुणध्वजः। 
मङ्गलम्पुण्डरीकाक्षः, मङ्गलायतनोहरिः॥

When you should do this Puja: Starting of any activity like education, marriage , for attaining wealth and peace ,whenever there are obstacles and delays  in life

Benefits of this Puja: The Puja removes all obstacles facing the  family, and  blesses with prosperity  , whatever wealth or property under dispute can be  redeemed if this Puja is done.