Click on the pen and use space to draw and arrows to move your pen. G to erase.
https://www.google.com/search?q=pen&source=lnms&tbm=isch&sa=X&ved=0ahUKEwifkoDbicfbAhWOnFkKHdOqBl4Q_AUICigB&biw=1280&bih=615#imgdii=9bRfaQJFS5DiCM:&imgrc=QKdpN49d3zR4-M: (For pen) https://www.google.com/search?biw=1280&bih=615&tbm=isch&sa=1&ei=RAocW7DdBuKc5wL-mZCQAQ&q=eraser&oq=eraser&gs_l=img.3..35i39k1j0l2j0i67k1l3j0l4.45593.46692.0.47223.6.6.0.0.0.0.162.532.5j1.6.0....0...1c.1.64.img..0.6.529....0.mQHRrlNsMTU#imgrc=m0NFF1bAm_MSZM: (for eraser)
