The problem I want to predict is what user will buy from the retail company who is hosting different type of products, I want to predict this at user level say user1 will buy sony camera, user2 will buy lenevo laptop etc. Which method and techniques will be used for it?
To start with, if the no. of products that the retailer is selling are limited (like 4-5 ) you can simply work on it as classification problem for these products as categories for each user.
Otherwise, as might be the case if the number of products are large, take all the products for each user ( create a column for user and one for products. Repeat the same user as the no. of product times) and make a outcome variable as 1 or 0. Then its a classification problem as well.
You will definitely need to add certain features to it like amount of money spent by user on that product, price of user, etc .
Hope this helps.