What you will see below takes a little explanation. This is work, a piano concerto, that in all likelihood started out on the composers table as 'scored' for two pianos..and you can see the first and second piano parts as follows. The first part (the top) is the solo piano part. The second part is either to practice to or, in Prokofiev's case, "orchestrate". Orchestration is assigning the notes to instruments of the orchestra or whatever combination of instruments the composer wants. Piano is often thought of as a "mono-color"...that is, it has one basic sound - that of a piano. An orchestra has nearly infinite colors drawn from the combinations of instruments. Orchestration is picking from these instruments and therefore 'colors' to enhance the effect of the music. It is a big deal. Some composers were great at it. Others were very bland. Prokofiev was pretty great.