The Sewing Machine is used with Cloth in the cloth slot (hey, at least that makes sense!) and just about anything else in the top slot:
fruit
vegetable
mineral
artifact
ore
fish
forage
animal product
artisan good
and more...
except for Tools and most Quest items.
Try it out and see what you make. Frankly I ignored this part of the game when v1.4 came out and introduced Tailoring, I thought it was a lame update. Yeah I'm quite used to getting things wrong but even by my standards that was a pretty bad take!
Tailoring is fun and if you do Emily's Rock Rejuvenation quest on the Special Quest Board, you get a Sewing Machine of your own for the Farmhouse! For me that's like getting to work from home instead of dealing with that awful commute. Even better that I not only don't have to dress for work but I can spend the time making the dress instead!
Tailoring is one thing that I encourage the use of the Wiki for as there are hundreds of options and no guide at all in-game to what you'll make so if you're looking for that classic '80s look and don't have 100s of Cloth to spend finding that the Cactus Fruit makes the 80s Shirt, it's just better to look it up. Though it's also fun to simply toss different things in the Sewing Machine and see what you get!
Also the Sewing Machine can double as a poor-farmer's Dye Pots as you can put a dyeable piece of Clothing (only ~1/3 of Clothing items are dyeable) in the Cloth slot and something that works as a dye in the top slot and it will color the Clothing item. Some dyes dye it all to their color in one go and some need 3 passes with the dye to achieve the final deep color, so you can experiment with shading. The Dye Pots are much easier to work this way as they have a fine-grained color slider but I've already expressed my dislike for The Commute to the Dye Pots. Also I like to Tailor at the end of my day and the Sisters' House is closed by then.