通过+ channel or certain way（朋友/网络...) + verb
我通过朋友认识她 I know her through my friend (my friend help to introduce us know each other)
我通过朋友见到她 I meet her through my friend ( my friend help arrange the meeting so that we can meet)
我通过网络学习汉语 I learn Chinese through Internet
由+somebody+(来）verb the action is done by sb.
会议由我来主持 The meeting is chaired by me
这个工作由他来完成 The work will be finished by him