Let's talk about the different symbols that are found in music that show you when to get loud or soft.
First, we have "Forte", in music this is shown as the cursive "F" we see above. This symbol means loud in English.
Second, we have "piano" in music. Not the same as the actual musical piano instrument. This term "piano" is show through a cursive "P" in the music. Piano means to be quiet.
The next symbols we have are mezzo piano and mezzo forte. These two symbols are shown by a cursive "M" and "P" for mezzo piano and a cursive "M" and "F" for mezzo forte. Mezzo means to be half. For these terms to be half soft and half loud.
For more information on understanding out these four symbols check out this website for more information: http://www.dummies.com/art-center/music/how-to-deal-with-dynamics-in-music-theory/