I suspect I'll regret this later, but I'm going to assume you aren't trolling...
My First question is: What's a block? What does it do/what is it used for?
A block is a set of transactions that are added to the bitcoin public ledger to form a consensus on transaction order and prevent double-spending of a transaction input.
I'm guessing that's something that you mine? I really don't know.
The process of gathering a set of bitcoin transactions together into a block, performing the necessary proof-of-work, and broadcasting the completed block is commonly called "bitcoin mining". In exchange for doing this work, the protocol allows the person (or group) to create a special transaction in the block that assigns 25 new bitcoins (soon the be reduced to 12.5 bitcoins) to themselves.
My Second question is: What's a hashrate? (E.g kH/s or whatever)
The proof-of-work for bitcoin requires repeatedly that the block header be changed slightly and then SHA256 hash of the block header be calculated until a hash value is found that is lower than the current target. The faster you can calculate the SHA256 hash, the better chance you have of finding a result with a low enough value in a given amount of time. The "hashrate" is the number of SHA256 hashes that your equipment can calculate in a given amount of time. It is typically reported in hashes per second.
KH/s = kilohash per second (thousand hashes per second)
MH/s = megahash per second (million hashes per second)
GH/s = gigahash per second (billion hashes per second)
TH/s = terahash per second (trillion hashes per second)
PH/s = petahash per second (quadrillion hashes per second)
Is there a certain hashrate to btc ratio?
Generating bitcoins is a random process. You could get lucky and find a block solution with the first hash you try, or you could get unlucky and have to try more than 830000 petahash. On average it takes 829194 petahash to find a block solution. Since blocks currently pay approximately 25 BTC, that means that the average ratio is about 33168 petahash per 1 BTC. So, if you can calculate 33168 petahash per day, you'd earn an average of about 1 BTC per day. Since there are 86400 seconds in a day, you'd need about 33168 / 86400 = 0.3839 PH/s (which is about 383.9 TH/s) to generate an average of 1 BTC per day.
My Final question is: Are cloud mining websites worth it?
No.
Most "cloud mining" websites are Ponzi scams. They don't do any real mining at all. They just take the money from the new people that sign up to pay the people that signed up previously. Eventually they run out of new people willing to sign up and they collapse and almost everybody loses all their money.
There are a few "cloud mining" sites that are actually mining, but they almost always charge more per hash than you will ever earn. They count on the fact that people foolish enough to consider cloud mining won't do much research into understanding the process and won't understand the long term effects of things like the subsidy halving and the difficulty adjustment.
Can you earn much from them?
You'll almost always earn less than you spend in the long run. Be VERY careful and VERY certain that you're going to come out ahead before you waste your money on any of them.
Are there any vouched for/trusted cloud mining sites?
You'll always be able to find people that will vouch for some site, and people that will trust some sites. That doesn't mean they are right.
I really wanna invest a small amount ($20 max) into something to keep it ticking by and hopefully get a bit of profit by the end of it.
If you think bitcoin has a lot of future potential, then you can buy $20 worth of bitcoin and then just hold on to it. If you're right then the demand will increase which will cause the exchange rate to increase. Then someday, you can sell your 0.0455 BTC for a higher amount than you bought it for. Any other "investment" available to you with $20 worth of bitcoin is going to be a pretty high risk (more of a gamble than an investment).
