Legalities of using data/information from external websites

I have a product idea that would gather information (ratings) from different websites and display them all in one place. It would show the name of the website the rating is coming from and have a link to that website for the user to read more info. This information is free and available online, so I don't know if it is free to use, or if I have to try and contact each organisation to ask them for permission, and how that whole process of acquiring data would work and how I can pull that data etc.