Congress.gov is the official source for federal legislative information. On the main page, change the pull-down menu on the left to "All Legislation." Enter your keywords, topic, e.g., "veterans", "border security," "mental health," "child nutrition," etc. On the results page, use the facets on the left to limit your search to specific Congresses and Status of Legislation "Became Law."
You can also BROWSE public laws-select the Public Laws link under the heading "Bill Searches and Lists" located below the search box. On the next page, limit by the facet "Subject-Policy Area" on the left. You can narrow even further by selecting a particular session of Congress.