The part that will take the most time to do, depending on your connection speed, is when you goto upload MyBB to your server.
FTP is easy! All you need is an FTP program which you can either get form your host or by downloading a 30 day trial form a third party such as CuteFTP, alternatively you can purchase it if you so wish to, but a 30 day trial will be sufficent for uplaoding MyBB.
Once you've installed your FTP program, you'll either find a wizard will appear asking for details about where you want to connect to. Or you'll find that you'll get a tool bar across the top with 3 or 4 boxes asking for host, username, password, port (this isn't usally displayed, and if it is, a number 21 should displayed in the port box).
Information for using the FTP program, will be available by going to Help in the tool bar. Also your FTP account information should be available from your webhost.
Now installing MyBB isn't that difficult! Just read the manual that is bundled in the download for MyBB and its all explained clearly there.
The stuff that throughs people is the CHMOD side of things, this is dependent on the operating sytem of the web server that your site is hosted on. Usaully its operating sytems other than Microsoft, such as Unix or Linix. BUT if its a Windows Server then you don't need to bother about CHMOD'ing. You can find out what operating system your host is running by either emailing them or by looking at their FAQ on their website.
Then its the Database side of things! MySQL.
Most Webhosts will have a web based program for using MySQL, which is a script called PHPMyAdmin and should be accesible by going to
http://mysite.com/phpmyadmin/ or your site may have a control panel with this in.
The details for accessing phpMyAdmin or to manage your MySQL databases should be provided by your webhost.
phpMyAdmin is an easy tool to use, just log in with your username and password you recieved by your webhost, once logged in you'll find a box with create database next to it, typein there MyBB for instace and click create!
And bam your database is created! in secounds!
When you goto install MyBB and it askes for database information, you'll know what your username and password would be as its the username and password used for accessing phpMyAdmin.
And the database name is MyBB as that si what you typed in the Create database box, when you logged in to phpMyAdmin.
Again the manaul will explain what to do!
You didn't need to know a thing about PHP nor MySQL either to setup MyBB as its just a click and type! MyBB does all the hard work!
Hope this helps!
NOTE: your webhost should be able to pass information on to your for accessing MySQL, or using the tool they supply for managing your MySQL databases.