Now press down gently on your foot peddle and the machine with start to sew. Start with just a few stitches and then lift your foot off the peddle again.
Now you should press down on tho button (if you machine has one) and it will do a few stitches back in the opposite direction. This gives you a nice secure start for your sewing and is a good idea whenever you start a line of stitching. When you get back to where you started press down on the foot peddle again and sew a long line of stitches. Guide the fabric under the machine, it will be pulled through automatically but your job it to try and get a nice straight line. Get a feel for the machine by pressing gently at first and then harder and see if you can start to control his fast you'd like it to go. Don't worry if your line isn't straight just yet, it does take a bit of practice.
You can draw some lines on your fabric with a dressmaking pen/dressmakers chalk and use these as a guide for sewing straight. I would recommend trying to keep the edge of your foot in line with the line (as above) rather than your actual line of stitching along your line. When we sew a real project we would usually stitch a certain distance away from the edge rather than along a particular line. So as you press down on the foot peddle keep your eyes on the line and try to keep it in line with the edge of the foot.
When you get to the end, use your little button (or your dial) to sew a few stitches in reverse to secure then end, then lift up the foot, pull our your fabric and snip the threads. Tada, your first line of stitches! Now have another practice until you start to be able to do all of that without having to read the instructions.
It is also good fun, and great practice to try and sew along some curved lines too. In the same way draw some curves on your fabric and have a go a sewing next to these, keeping the drawn line in line with the edge of the foot. Don't forget to sew a few reverse stitches at the beginning and the end.