You've had a sewing machine for years and it's time to move to a new machine. It seemed super when the dealer shows the machine, until you go to actually sew and the pressure foot that you're used to as a guide isn't with the machine. The dealer showed you that your new machine has many needle positions. Those needle positions replace that machine foot and give you more control ... even if it takes time to adjust to the change, it's worth it!
If your machine has zig-zag capabilities, it most likely has needle position adjustments. The photo shows three positions. Most new sewing machines offer more than shown here.
The needle position option allows you to use guides on your presser feet and adjust the position of the sewing machine needle, to have the stitching placed exactly where you want it.
On almost all machines, using a straight stitch and changing the width of a zig-zag stitch on the machine allows you to sew a straight stitch with the needle position changed. Align the machine foot where you want it and change the "zig-zag width" to gain the stitching line that you want.
Presser Foot Guides to Use With Needle Positions
Your eyes should always follow a guide on the machine or the foot, not the machine needle to achieve straight stitching. Take the time to practice on scraps of fabric to gain your comfort and confidence.
Look at your feet and find the lines or markings that you can use as a guide. The feet shown here are just two of many examples that could be used to show the many options on different feet for different machines.
Using a Presser Foot Guide With Needle Position
Using a guide on the presser foot and changing the needle position allows you to sew a distance from the seam that you choose. Under-stitching and top-stitching stitches can be placed where you want the stitches to land.