Our first steps tour and our frequently asked questions will help you a lot after registration. They explain how to customize the interface (for example the language), how to upload files and our basic licensing policy (Wikimedia Commons only accepts free content). You don't need technical skills in order to contribute here. Be bold contributing here and assume good faith for the intentions of others. This is a wiki — it is really easy.
More information is available at the community portal. You may ask questions at the help desk, village pump or on IRC channel #wikimedia-commons (webchat). You can also contact an administrator on their talk page. If you have a specific copyright question, ask at the copyright village pump.
I noticed you've uploaded multiple images that differ only in size, and I thought I should draw your attention to a certain feature of our software. MediaWiki, the software which drives Commons and other projects like Wikipedia, is able to handle reducing the size of the images automatically. For example, even though File:Red Apple.jpg is a very large picture (2418 × 2192 pixel), MediaWiki can automatically generate thumbnails in all sizes (example: 50-pixel thumbnail). You can include a thumbnail of an image in a Wikipedia article using
[[File:Red Apple.jpg|thumb|Description here]]! If you need it a bit smaller in width – for upright / portrait aspect ratio images – use
[[File:Red Apple.jpg|thumb|upright|Description here]].