Launch PowerPoint and either choose a template or select Blank Presentation.
Specify the dimensions of the poster before adding content by clicking on the Design tab, then clicking on Slide Size, then Custom Slide Size.

In the Slide Size dialog box, enter the width and height for your poster. Suggested dimensions are 24x36 or 36x48 (most common). Always check the size requirements set by the event, One of the sides must be 36" or smaller to print at the Sirota Memorial Library. Choose landscape or portrait.

If you want to use a background color other than white, you can change it. Click on the Design tab, then click on the Format Background icon.
To add text to your poster, click on the Insert tab and choose Text Box. Then click and drag to create a text box. You can change the box size and location later.
To add an image to your poster, click on the Insert tab and click on either the Pictures, Online Pictures, Screenshot, or Photo Album icon depending on where your image is stored.

To add shapes or lines, click on the Insert tab and choose Shapes . A dropdown menu appears with many different shapes. Choose a shape, then click and drag to add it to your poster.
To add a chart, choose the Insert tab and click on the Chart icon. An Excel spreadsheet will open where you can enter your data. If you need to change something in your chart, you can right click on the Chart and go to Edit Data. The benefit of creating a chart in PowerPoint is that the Excel spreadsheet is saved with your PowerPoint file. You can change the data and the chart will resize automatically.

You can add formatted equations by clicking on the Insert tab and choosing Equation.

FINALLY! Save the file as either PowerPoint or pdf.