Nothing really happens here, you're just telling Turbo Pascal what you need for later on. Note that the end is followed by a period. Click here for a sample. In a sense, an executable statement is much like a phrase within the a sentence. Semicolon as a separator.
Every executable statement needs to be terminated with a semicolon.
Writing style - in my not so humble opinion there are two vital skills in writing style. This might sound obvious, but Turbo Pascal does not require executable statements to be seperated by a line break, only by a semi-colon. The other skill is indenting. Basically everything between a begin and end should be indented one level. As we learn other programming structures, you will be indenting further levels.