What can I do to lower it?
This article should help: https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/lower-acid-soil.htm
How can I make my alkaline soil more acidic? Is Epsom salt good for acid loving plants?
This article will help with acidifying the soil:
Epsom salt is good for all plants. It helps add calcium to the soil, which plants need. Here is more information: https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/epsom-salt-gardening.htm
I want to know exactly what is sphagnum peat moss, Perlite, and Vermiculite? I want to know about these in detail, and how or where I can get them to make my own soilless mix for indoor plants.
Oh, and all are available at your local plant nursery or hardware store that sells plants.
Peat moss is a substance that is made from either sphagnum, which is a kind of hanging moss, or peat which is a buildup of decayed swamp matter that is mined and then sold.
Perlite is a type of exploded volcanic glass that holds water and air well.
Vermiculite is similar to perlite and is an exploded stone.
I have heavily compacted clay soil in my garden of about 170 sq. ft. (26'L x6. 5 W. . . with about a one foot depth). I only want to plant flowers and/or ground cover. I heard different stories on using pure Gypsum to break down the clay, (Armstrong) or Home Depot told me to use only AMEND, that already has the gypsum in it, along with nutrients. I made a 1/2 inch screen wire on a 2 x 6 and am sifting through the bigger, hard to breakdown clods, big rocks, old roots, and allowing old pea gravel through the screen to make for a better looking, more uniform clay dirt base before adding soil prior to planting. One person told me I'm working too hard and just use the gypsum to break it down. What type of soil is needed to plant? Manure with no nutrients , top soil, or just basic garden soil?
Here is an article or two that you may find helpful: https://www.gardeningknowhow.com/special/organic/compost-for-organic-gardens.htm
Percent of organic matter should optimal planting soil contain?
To tell the truth, you can go with up to 100% organic material and still grow well (this is essentially what potting soil is). The ideal minimum is about 30%.
How do you know what soil is best for your plants?
All plants benefit from healthy soil--most of which requires the addition of organic matter. Here is an article that you may find helpful: https://www.gardeningknowhow.com/special/organic/the-importance-of-soil-for-an-organic-garden.htm
I need to do a lesson with soil, soil with sand, and soil with clay. I have not been able to find soil with sand and clay. How can I possibly make soil with clay and sand? Where can I buy it?
I'm not sure where you can buy clay soil, but many home and garden centers have sand. Here is an article or two that you may find helpful as far as locating these soil types in your yard (or nearby): https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/amending-sandy-soil.htm