Airdrops are just one kind of advertisement. By signing up or promoting or referring to friends the currency will offer some tokens. After the ico period the coin will list in the market and the tokens will be added in the wallet.

I want to invest  $500 in crypto market. I have studied a little bit about the market. As I am not experienced in this sector, I am a little bit confused where should I invest?
I know my capital is too little.
Would it be wise to invest in Alt coins?
Or should I go for the ICOs?

You haven't discussed elaborately about your startup/project. Weather it is useful to society or fruitless, without knowing the ins and outs can't suggest anything.

As it is summer, hoodie is not usable here. so I will buy a T-shirt. I am cryptohead so bands, caps and others also seems interested.

It's really great to listen to this news. More online shops should adopt it. I heard about a currency through which i can buy Tesla cars.

I have not proper knowledge on it. And i didn't face it before. What are you taking about?

Investing in ICO is not for all. Proper knowledge and experience needed before investing.
1. the background
2. who are running this?
3. business strategy
4. future prospect
Considering these cases and others then it is better to invest in ICO.

Mining is worth if the mining rigs are available in the country. Again some more factors matters like the electricity cost and temperature of the country.

Money laundering was in the past, prevails now and will be in the future. So bitcoin is responsible for money laundering it is not completely true. It can't be a reason to ban bitcoin.

Those who were holding it for long since. As the price is slightly down they think it is to sell it right away.

In my country homeless people who lives in the street can't manage a days three times meal properly. How can they use bitcoin?
They are mostly illeterate and have no internet access.

I am exciting to hear this. I love KFC chicken. Hope soon in my country KFC will accept bitcoin 

Banks and other governmental organizations are trying to ban bitcoin thinking of losing the power to control over individuals monetary activities. But soon the banks will offer bitcoin deposits and transactions to compete with the market.

Bitcion being volatile for the FUD and bans form government. Bitcoin is a digital currency a best alternative of the fiat money. It will stabilize soon.