PowerPoint (PPT) is an easy way to make attractive poster presentations.  Here are the basics.

Start off with a blank slide.  Do this using the Home tab, and under Layout select Blank.

1. Now, you're ready to start designing your poster.  You will be creating a custom slide size (this will be the ultimate size of your poster).  So, in this case, you want a 24 x 36 inch poster:

1. Select the Design Tab in PPT
2. Select Slide Size on the far right-hand side
3. Select Custom Slide Size 

4. Indicate the desired poster size:  Width:  36inches   Height:  24 inches (or the other way around if you want a tall poster) 

2. Select the View tab, and under View click on the check boxes next to Ruler and Gridlines (and Guides if desired).  These will help you to align your text boxes, pictures, etc.

3. Click on the Insert tab and start adding content to your poster by placing text boxes, images, etc. in your poster as needed, and use your ruler and gridlines to help you line up your objects. 

Need more help. Check out this video: