When browsing the Web you may find text or images to be too small for you, and you may wish to increase their size or otherwise adjust the browser so you can properly see the content.
Though each browser has its own options for making text and images more legible, there are a few approaches in Safari that are a bit uncommon and not only help you zoom in and adjust what you are seeing, but also allow you to manage tabs and other content you are viewing.
The first option for zooming in Safari is to use the systemwide zoom option in OS X. By holding the Control key and scrolling up or down (or by pressing Option-Command-8 to enable zoom followed by Option-Command-plus/minus to zoom in or out), you can increase or decrease the zoom level in the system.
While convenient, this option does have some drawbacks. For one, it doesn't change the displayed image resolution, so as you zoom the pixels in the image will get larger instead of getting any crisper. In addition, this display mode will constrain the window to your desktop and require you to move your mouse around to view hidden content beyond the extent of your display.
As with most browsers, Safari contains a quick way to zoom in on content by holding the Command key and then pressing the plus or minus buttons. This will proportionally increase the size of text and images, though at times it may result in relative changes that can change the layout of the items on a page (especially if you have "Zoom text only" set in the View menu), but for the most part it should work just fine to make things more legible.
You can also use OS X gestures to zoom in Safari, and by pinch zooming you can perform the same content-resizing routine that can be done with the Command-plus and Command-minus hot-key combinations. This feature has an added benefit: if you are at the standard zoom level and zoom out, then you will go into a Tab-preview mode where you can scroll through and select the various tabs you have open. This option can be quite convenient for browsing the Web.
In addition to the pinch gesture, Safari supports and iOS-like double-tap with two fingers on the trackpad (or one finger on a Magic Mouse) to zoom in on a specific paragraph or figure. This option is similar to the content-resizing option, except that it will attempt to zoom in on a specific text field or other object to the extent of the current window.
Another option in Safari that is not necessarily a zooming feature is its full-screen mode in Lion or Mountain Lion. While this will not increase the size of content, in this mode you can take full advantage of pinch-zooming and other options to better view your Web pages.
The final option is likewise not a true zoom, but can make reading some content more pleasant, especially if a page is cluttered with ads and links that distract you. If the browser detects that you are viewing an article, it will offer you a Reader mode that appears as a blue button labeled "Reader" in the Safari address bar. Clicking this will bring up a simply formatted view of the article that should contain relevant figures and images, but should omit all the social media buttons, ads, and other links that are common throughout the Web. This feature works well for the most part, but there are some instances where it does not render them correctly.
The reader is especially pleasant to use when Safari is in full-screen mode.