If (the) teachers speak (in) English without any gestures,objects,pictures and so on at (first->beginning) when they (have->give) a new lesson,(the) student (maybe don’t -> may not) understand clearly what the teachers (said -> say or are saying).
Right one:
If teachers speak in English without any gestures,objects,pictures,and so on at beginning when they give a new lesson,students may not understand clearly what the teachers are saying.