Templates (as of Office 2007) are basically empty presentations with design elements, backgrounds, content placeholders - everything but the content. You cannot apply them to an existing presentation. You can choose one before you get started, or you can copy and paste text into a template. (If you don't have a particular template you want to use, you may want to use themes - you can apply and reapply as much as you want.)

New from template

File > New > Sample templates OR Recent templates

Use template from existing presentation

File > New > New from existing

Find more templates

Can search from File > New or download outside of PowerPoint.

Need to copy in text? Best to go to Outline tool and paste in from there.

Themes are how you apply a design to all of your slides. Go to the design tab and select a theme.

They have a live preview, so you can see how it looks before committing to the change.

You can change the font here:

     Click on Themes > Fonts > Create New Theme Fonts. Select the fonts you want for the body and headings.

Adjust the colors

     Click on Themes > Colors > Create New Theme Colors

Background

     Click on Background >Background Styles

You can select one from here or go to Format Background for more options (custom color or a picture/texture)

NOTE: to change the background on only one slide, right click on that slide and select Format Background from there.

If you want to create your own theme/template, you may want to edit the master layout.

Go to View - Master view - Slide master

There is a top level master slide, anything here will be applied to all layouts and slides. There are also layouts under this top-level master, so you can have have a different layout for the main title, the ending slide, section headers, body slides, etc.

Note: you cannot delete a layout that's in use. To see if a layout is in use, hover over it to see which slides are using this layout.

You can insert text boxes here or a background. You can also apply tweaks here such alignment and turning off/on autofit, which will apply to all slides.

You will not be able to change anything in the master layout from the slide view. SO make sure anything you put here is to be applied to all slides. (or all slides of a certain layout.)

To add a new slide of a certain layout, go back to normal view. Go to home - new slide, click on the arrow on the bottom and insert the layout you want. To modify the layout of an existing slide, click layout (next to new slide).

Formatting the text box

    Right click on Text box > Format shape

    In left sidebar go to text box.

You can turn off autofit here to guarantee a consistent font size. (best to do this in master view)
You change vertical alignment here. It is sometimes easier to line up boxes with each other if you choose top or bottom alignment.

Change spacing between lines and paragraphs

     Go to Home > Paragraph and click on the small arrow in the bottom right hand corner.

Spacing before and after refers to paragraphs, line spacing is every line.
You can also change the space between bullets here, under indentation and special.
If it says first line, switch to hanging (this is where the text stays right of the bullet, instead of wrapping underneath, and it looks much cleaner).

Transitions are from slide to slide. You can apply these from the transition tab. (Examples include fade, dissolve)

Animations can be applied to a line of text, picture, or just about any object. You can apply these from the animations tab.

You can order your animations in the Animation Pane, as well as setting your timing and triggers.

Remember to use these sparingly! Motion attracts the eye, but too much can be distracting.