I can second the 'make a calculator' as a place to get started with this, that's a solid project to get the basics of flexing -> parsing -> evaluation. Helped me learn a ton when I first wanted to approach this problem.

On a side note, I pretty annoyed by the prevelance of 'So you want to be a <insert something here>' titled articles. It's so common around now and just doesn't seem to express good intent about what is actually going to be in an article at this point.