1) Concerning your first question (Yo he). It corresponds to the tense called "Pretérito Perfecto" in Spanish, which is formed using the structure:
S+ verb haber + participio pasado + complement
Ex: Yo he usado el libro (yo lo he usado) / I have used the book (I have used it)
2) The other question just refers to a verb: llevar, which depending on the context means "carry" or "take" . The verb llevar is not used to form the "pretérito perfecto", so you don't say "yo llevo usé" but "yo he usado". The latter, as you can see, follows the structure S+haber+past participle
Ex:
Yo he usado ese libro para buscar información
Hope it helps. Saludos!