Committee reports are probably the most useful. They often provide
Hearings may also be useful as they
Limit search to Legislative Histories (left side under Document Types: uncheck "Select all" then check Legislative Histories)
If possible, search by Public Law number - for example, P.L. 106-169 - for most specific result. Otherwise search by keywords from the title of the legislation or the policy topic and select the appropriate Congress or years.
Within the legislative history, useful items include
For full text of reports and/or hearings, click on CIS Number link to go to the report or hearing entry, then go to Links To section to retrieve the committee report or the available transcripts.
In the report(s), look for sections that may discuss purpose of the legislation, background and/or need for legislation, explanation of (significant) provisions, etc.
Hearings may include prepared statements and/or question-and-answer sessions
When searching, consider using quotation marks to identify key phrases; for example, "foster care"
Results can be sorted by relevance or date: new to old
When mousing over entries in the search results list, hover over the arrow to see a brief abstract and links to full text
Public laws affect the general public or classes of citizens. Public laws are numbered sequentially within each Congress; for example, P.L. 106-169 is the 169th public law passed in the 106th Congress.
Googling the title of the law (AKA act) is one way to identify the P.L. number of a law.