Rules for good comma placement throughout long sentences.

proper comma placement

I'm trying my best to improve my writing. One substantial area where i always loose points is comma placement. for instance here is a small cutout of a paper where i was marked for improper comma placement.

Tools are not just physical items held in your hand. Not just limited to hammers and nails. Skills are tools of the mind. Just like their physical counterparts, shouldn't they be included in ethical consideration too? After all, the difference between a mason and a man making a giant mess is his ability to lay bricks properly. In many ways skills provide much more to the user than any physical item can ever hope to. Skills can be purely analytical, such the skills I'm building by going to college. Discovering new ideas that have given rise to tools such as differential equations and linear algebra. The pure logical building blocks to engineering.

Is my professor being difficult? When i play it through this website it sounds alright to me. Are there any particular rules i should follow?

readmytextto.me/share/8Hi7DT

A bigger problem I see are your sentence fragments - you have three that I see:

Not just limited to hammers and nails. - this is really lacking both a subject and verb - something is not just limited
Discovering new ideas that have given rise to tools such as differential equations and linear algebra. - this is lacking a subject - who is discovering?

The pure logical building blocks to engineering. - this is just a subject and needs a verb

The only comma I see missing is
"In many ways, skills ..."

Commas are very difficult and I think somewhat subjective in many cases. There was a whole book written about commas a few years ago: Eats, Shoots and Leaves. As you implied, the main rule is to put a comma wherever you would naturally pause when reading the sentence. But for ESL students, this is not always the biggest help. Maybe others have some tips.

NCS, using and placing commas in sentences isn't all that difficult. If you have 2 connected ideas to present in a sentence, use a comma instead of a connection word. Read the paragraphs and and place a comma wherever you stop to take a breather. That is the natural reading pause point. Your essay does have periods in places where commas should be. That's why the sentences came across as too long. The comma is meant to divide the sentences that come across as overly long. Beware though as improper come placements can also cause run on sentences and you don't want that. Basically, knowing where to place the pause (comma) in your writing is a skill gained over time. You may be taught the theory of the punctuation usage but unless you constantly practice, the natural or second nature use of the comma will not be developed. I suggest that you practice the skill using more exercises or online free practice sites. It's available in Google. Your teacher is right. You just need more practice in order to properly develop the use of the punctuation Mark in given sentences.