Is there any way in which I can make investments online with say some money from my PayPal account, and continue this completely online? If I can, what is the minimum amount of money that I would need to have in order to make the smallest possible investment (as a start)?

I don't understand your question. Are you talking about break-even analysis?

What's that? Look, I don't have any knowledge of this. I was asking about any type of investments I could do, like the stock market, or a bank, or anything, but which can y carried out online (completely).

There are some investments that can be done online.
They usually use e-gold not paypal.
Be advised that 99% of the so called high yield invetment programs are scams.
Discussions of them can be found at talkgold.com gold-horizons.com and web-life.org
This is an arena in which a lot of money gets lost but there are a few real offerings.

Thanks, I'll take a look at those!