"Policy" is a generic term that can describe a wide range of formal or informal documents that describe proposed action or guidelines of behavior. Policies can be very local in nature (e.g. a company policy), or they can be very broad recommendations upon which laws can be based (e.g. environmental policy).
Think tanks are institutes that research and produce policy documents and recommendations, and can be influential in politics and public opinion.
"Laws" can refer to legislation (i.e. laws passed through government bodies), case law (i.e. laws passed through courts), or executive orders. There are different places to look for different types of laws.
Search hack: Use Google, and type site:(name of government website you are searching) "phrase of something you're searching". Doing this will take advantage of Google's search algorithm to find specific laws, bills, or other formal proposals from government entities. For example:
site:congress.gov "reproductive rights"
These resources can also help you find legislation: