First of all, login to your Dashboard, have a click around and get the geography. Probably, most of the things in the Dashboard you won't need to touch to maintain your site but it's a good idea to get to know where things are.
All of the things you will need to use are in the grey sidebar on the left. The contents of your sidebar may have different things in it than the images in this document - that doesn't matter, everything works in the same way and the images for this document were taken from a different website's Dashboard.
WordPress is very robust so please have a good click around the Dashboard and become familiar with it - you won't break anything! If you do something wrong it can always be undone - everything is fixable.
Download the PDF below for a handy printable guide to refer to.