The selection tool (black arrow) selects, moves, and resizes objects.
The direct selection tool (white arrow) changes the inside (fill) and outline (stroke) of text boxes and shapes.
The text tool adds and edits text. Most often you will probably use text boxes for your text. The boundaries of a text box control the flow of characters; when text reaches a boundary, it will automatically wrap to fit inside the defined area. Illustrator does not have a spell check feature. If you have a lot of text on your poster you may want to type it in Word and copy it to a text box in Illustrator.
The rectangle tool creates a predetermined shape in your document. The colors of your shape are determined by the colors selected in the stroke and fill area of your toolbox.
The fill color refers to the area enclosed by the outline (inside of a text box or the inside of a shape).
The stroke color refers to the outline of a shape or text.