The use of pictures in Joomla is a bit different from the methods you are used before, so you need to learn new habits here. But the first problem is usually not that, but how to upload those pictures to the site.
First of all we strongly recommend some additional components to your Joomla site, if you don't have done allready.
On the top of these recommended add-ons are the file/FTP managers joomlaXplorer/Ninja eXplorer/OSE Filemanager and the WYSIWYG editor JCE. We will use both recipes here.
We also recommend to arrange your pictures in subfolders for better organization and easier retrieval. To be used, your pictures must be placed in the /images/stories directory of your Joomla install, or in subdirectories of this directory. You can assign the subdirectories do given content sections/categories if you wish, but that's the subject of another tip.
Having all the above handy, generally you have at least 5 ways to upload your images. I grouped them using certain criteria, but the order is mandatory, pick the one you like!
Here they are:
a. supposing you want to upload more files for later use
You can choose one of following methods:
1. Use JoomleXplorer/Ninja eXplorer/OSE Filemanager: From Components menu, select the corresponding link, navigate to the directory you want and use the 10th icon from left (The globe with the green up arrow) to upload your files. You can upload them in batches of 10.
2. Use the File Manager from your hosting cPanel. The procedure is similar, you navigate to the corresponding directory (the main difference is that the file structure is one level deeper, you need to go to /public_html/images/stories directory or one of his subdirectories) and the number of files you can batch upload: 12.
3. Use your favorite FTP program. Nothing to add here, the directory is the same, and if you're a versed FTP-izer, you know how to proceed.
For the last two solutions there are some slight differences on side effects compared with Joomla based solutions, for your future reference I'd recommend you to read this tip!
b. you want to upload one file [anyway, not too many]
The choices you have are:
4. Upload them from the Joomla's MediaManager. The link to the Media Manager is in the second menu from left in the Joomla's admin interface, the Site menu, 3rd item from top. The interface defaults to the /images folder of your Joomla Install, from here you should navigate to the corresponding subfolder [at least the /images] and upload your picture(s)
5. You can upload single files (or more, one-by-one) from your editing interface, directly from content editing interface. JCE editor, which you have installed and you use it by default has an embedded file manager, (the 7th icon from left in the last [4th] row of editing interface, the file icon with a chain on it) which opens in the /images/stories folder and also let you upload your files of all kind in the desired place.