Poco a poco means "little by little." It is a common qualifier and means that this section is to build and build, little by little.
Molto means "much" or "very" and is another common qualifier. Whereas previously the notation called for poco a poco in building the intensity, molto now commands a quick building of intensity.
Dim. sempre or diminutive sempre literally means "always small." Also note here the vertical squiggly lines. This means that the notes should be rolled or played in order from the bottom most bass note to the top most treble note, quickly of course.
The horizontal squiggly line here preceded by the tr means it is a trill. I believe I already covered this elsewhere. I wanted to draw attention to the "8" here coupled with what looks like a backwards long-division sign. This means that these notes are to be played an octave higher than they are written. That is your musical notation lesson for the day!