Your company may already have a library of icons to use in presentations.

However, if those aren't available to you, PowerPoint provides an extensive library of icons.

Go to the insert tab and then over to icons or press alt + N + N S.

Here you'll find a wide variety of icons to choose from, all in solid or line style.

The icons are in SVG file format, so you can do more editing to them than simply changing the colour or size.

If you right click on an icon and then click convert to shape, the icon will then be broken down into parts where you can then colour different parts, remove parts, or even have greater flexibility in combining a few different icons and using parts from a variety of them.

When using icons for presentations, be sure that the style of them is consistent.

Try to either use solid or line icons and that the design of them is consistent.

External websites can be great to source icons from, but it becomes easier to be inconsistent with these as every designer will have their way of creating icons, be it the thickness, the radius of edges, and more.