The following are links to Early Church History documents available online, in English translation, for free. In some cases, there are better translations available in print, so for serious scholarly publications, you will want to consult those. But for introductory purposes, the following links may be helpful.
• The Works of Aurelius Augustine - (additional volumes are included above) • The Anti-Pelagian Works - Part 1 (= Volume 4), Part 2 (= Volume 12) (T & T Clark, Marcus Dods 1872 edition) (archive.org) • Works Related to Manichean Heresy - Marcus Dods edition (archive.org) • Works Related to Donatist Controversy - Marcus Dods edition 1871 (archive.org) • On Instructing the Unlearned; Concerning Faith of Things Not Seen; On the Advantage of Believing; The Enchiridion to Laurentius - (archive.org)
• Tertullian • Tertullian.org - includes excerpt from many versions of each of about 30 of Tertullian's works • Against Praxeas (google book pdf: 1920 edition) • Apology (google book pdf: 1850 edition) - there are many 19 C versions • Apologetic and Practical Treatises (google book pdf: 1842 edition) • Concerning the Resurrection (google book pdf: 1922 edition) • Writings of Tertullian in Ante-Nicene Fathers, Volume 1, Volume 2, Volume 3, Volume 4 (google book pdf's)