This most essential teaching of the Buddha offers countless possibilities for inquiry, reflection, and practice. Resources to this end are found in various places on this website. Below are links to those pages.
Talks by Ajahn Buddhadasa on 4 Noble Truths
2009 Study Course on Practicing with the Ariya-Sacca (by Santikaro)
Santikaro gave a talk on the structure of the Four Noble Truths and using them as our Framework for Studying Buddha-Dhamma (MP3, 9.9 mb)
Reflections on the busyness so many of us grumble about used the 4 Noble Truths as the framework for inquiry (MP3 to be posted)
Mahacattarisaka Sutta (MN 117) & Mahatanhasankhaya Sutta (MN 38)