Complex sentence: Hoffmann began teaching at Buckingham Browne and Nichols in 1891 and a few years later helped establish the Alstead School of Natural History in Alstead, New Hampshire where for a timw he would spend his summer breaks teaching.
Split into simpler sentences: Hoffmann began teaching at Buckingham Browne and Nichols in 1891. A few years later he helped to establish the Alstead School of Natural History in Alstead, New Hampshire where for a time he would spend his summer breaks teaching.