MB of space - MB? Eh? Well, MB stands for MegaByte. This is basically the amount of storage space you will have. You can figure out how much space you will need if you spend a little bit of time thinking about what is going onto your site - how graphic intensive it will be, how many pages, any multimedia or music, etc. Make an approximation in your head and then add another 50. This will allow you to add on and expand. It's always better to have too much, rather than too little.
Pricing (Monthly/Yearly) - the payment plans are generally either monthly or yearly. Make sure, even if you want a year or more of hosting, to start with a monthly plan! If you give them $3/400 for a year, and then they end up being useless, I'll bet you that you won't be getting that money back. If you start with a monthly account, you can always upgrade to a yearly account. And if you can't upgrade and you're really worried, add up how much it will be for a year, and set that money aside to slowly add back onto your credit card every month.
Domain Registration - do you already own a domain name? A domain name is basically the www.yourdomainname.com. Most of web hosts will provide domain name registration in their packages. If you already own your own, you will have to transfer it to their name servers. Make sure this is possible! Ask them if they will do it for you, or ask for directions on how to do it yourself. If you don't own a name already, though, how many will you need? Will the one be enough? Do you need redirects; do you want extra names attached to sub-domains?
And then you need the actual name! If you're completely stumped, have no ideas, there are some really good places online which will create a list for you.
Make sure your name is relevant to what's on your site - people tend to get annoyed if your website is called "cool-cars.com" and it ends up being about cushion embroidery.