You can apply styles to an image in three ways:
1. Directly in the image tag e.g <img src="img_url" alt="alternative text" style="width: 100px; height: 100px... [virtually all other applicable css parameters here]" />
I rarely ever use this as it tends to take up a lot of space in the code of the page.
2. In the head of the page <head><style="text/css" />img {width: 100px; height: 100px; [any other applicable css parameters here]} The thing about this is, it applies those styles to all the img tags on the web page (except those with styling determined by 1 above). This can be both good and bad, it keeps the images uniform and changes are made in one place. This applies the same strict set of styles to all the images on the page but is limited to only the page it is on (not many cases where you would want that).
3. In an external stylesheet (my default option). This is easier to use as far as I am concerned. This can be achieved by linking the stylesheet to the page in the head by typing: <link rel="stylesheet" href="stylesheet_location" type="text/css" media="screen" charset="utf-8" />. That one sheet will determine the layout of all the pages in the website that have this stylesheet attached to it. Good if you want to maintain site-wide uniformity in design and layout and you can also carry out sitewide modifications from this one file. You can also go further by determining "divs" (this can also be done in 2 above) that are just "containers" on the page with specific styling determined in the stylesheet or in the div itself:
e.g. #divName {width: 800px; margin: 0px auto; (this centers the container [other attributes here] }. This is a div id and ".divName" is a class - classes can be used more than once on the page while ids are used only once (CSS rules). The can be achieved in the div on the page itself by: <div style="width: 800px; margin: 0px auto; (this centers the container [other attributes here]". In the page the style is applied only to that page and in stylesheet it is applied to all the pages with that div.
CSS attributes can be applied to almost any (X)HTML tag by <[html_tag_name] style="CSS attributes here"></[html_tag_name]>.
Hope I was helpful in outlining the principle to you. I'd be happy to help further with HTML and CSS. You can always send me a message or IM me.
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