Practice drawing the note. Don't worry about the notes you're writing. You aren't trying to compose a song. You simply want to get a feel for shaping the notes. Start with a blank sheet of staff paper, also known as sheet music paper. It consists of five lines and four spaces. Each of those lines and spaces represents a note name. Where you place your notes on the staff tells other musicians what note to play. Draw a whole note. A whole note is a simple circle slightly angled down. Once you've successfully drawn that, turn it into a half note by adding a small straight line extending from the note head up. It doesn't need to be a long line; just long enough to show a stem.
Turn the half note into a quarter note. A quarter note is a half note with the head colored in. Whole notes and half notes have uncolored note heads. Turn your quarter note into an eighth note by adding a tail to the stem. The tail is a small, curved line added to the side of the top of the note stem. Two or more eighth notes can also be written side by side and attached with a line running across the stems instead of writing them separately with tails. Make sixteenth notes the same way as you make eighth notes, except you need to add two tails, one under the other. Sixteenth notes can be linked together the same way as eighth notes can be linked together.
Write the notes on the sheet music paper. Up until now, you've only practiced drawing them. Now you should put them on the sheet music paper in bars. A bar of music is indicated on the sheet music by a vertical line that separates the staff into bars. Each bar needs to contain the correct number of beats. A whole note takes up an entire bar. A half note takes up half a bar, so you can fit two of them in a bar of music. You can put four quarter notes to a bar, eight eighth notes, or sixteen sixteenth notes. Bars of music can also be built using any combination of these values.
Practice writing music notes by referencing a standard piece of sheet music and copying the notes as they appear in the sheet music. The key is to make your notes readable. While there is a standard shape to the notes, many composers have distinctive ways of forming them, much like each of us have distinctive handwriting styles.