Most screen printing inks are ready for use right from the can. The ink should have a viscosity somewhere between honey and heavy cream. It definitely should not be watery. If the ink seems too thick, pour the amount needed to print the job into a clean can and add a small amount of reducer. Your screen printing supplier will provide you with data sheets for all the ink and ink modifiers they sell you if you ask, and these documents will have specific instructions.
Screen printing is like ski jumping.
Once you start, there's no convenient stopping place until the end. If this is your first time, you might want to unplug your phone, or at least turn on your answering machine. Place a practice blank in the registration stops, lower the screen and then pour about a cup of ink onto the screen between the image area and the side of the frame held in the hinge clamps. Spread the ink a little toward the top and bottom of the frame and then make one print stroke across the image area of the screen. Do this by holding the squeegee in both hands, placing it in the ink pool, tip the squeegee handle about 15 degrees out of vertical in the direction of the print stroke, push the squeegee firmly down and pull the squeegee toward you.