This is something that happens a ton. First
Liquid Yeast. Usually used in industrial bakeries. If you're using this, you probably already know more than I do.
Fresh Yeast. This is live and is measured in "Cakes." If you're baking every day and can't tolerate any sourness in your product, this is a good choice. If you Don't bake every day, this stuff is perishable and expensive, so probably not worth the trouble. If you're recipe speaks of "Crumbling the yeast into body-temperature water..." it was probably written for fresh yeast. By measure, bread will usually call for "one cake" for a pound (3-1/2 cups) of flour.
Active Dry Yeast. Recipes from the 1950s to the 1990s usually used active dry yeast. If you "sprinkle" yeast over body-temperature water, it was probably written for Active Dry yeast. By measure, bread will either call for "2 teaspoons," "one packet," or "a scant tablespoon," per pound of flour.
Instant Yeast. More Modern recipes use "Instant" or "Bread Machine" yeast. If you mix the yeast with the dry ingredients, it was probably written for Instant Yeast. By measure, bread will call for "1 teaspoon," for a pound of flour. If you aren't using sourdough, and you should, think long and hard about using anything except Instant Yeast in your bread. Mix it with the dry ingredients. No blooming necessary. If you keep it in the freezer it has the shelf life of Plutonium.
Sourdough. Once you have a good active culture, you can substitute sourdough culture for yeast if you do a bit of math. My culture at 100% hydration, so I use 200g of culture in place of 100g of flour and 100g of water. Start with a recipe you know well and substitute away!
So let's talk about substitutions into Instant Yeast, with a smidgeon of sourdough talk.
Cake yeast will be "crumbled into body temperature water" or similar. Sometimes you'll be asked to add sugar or flour or both and wait fifteen minutes to be sure it bubbles. If the cake yeast is mixed with warm water, substitute a teaspoon (or packet) of yeast per cake. Instead of mixing it with water, combine it with the dry ingredients. If the yeast is used to make a sponge or a polsh, simply combine it with the dry ingredients when you'd normally combine it with water.
Active dry yeast will be "sprinkled into body temperature water." Similar to cake yeast, some recipes will call to bloom it in water. Packet for packet, AD yeast and Instant Yeast are equivalent. Two teaspoons of AD yeast are equivalent to a teaspoon of Instant Yeast. Instant yeast requires no blooming or sprinkling. Merely combine it with the flour and other dry ingredients.
If the yeast is "Crumbled into water," then it's speaking of "Cake Yeast."
If the yeast is "Sprinkled into water" then it's speaking of "Active Dry Yeast (AD)"
If the yeast is combined with dry ingredients, then it's using "Instant Yeast" or "Bread Machine Yeast," which are identical.
Most recipes are scaled for a pound of flour and a cake of yeast (or packet of AD, or packet of Instant, or . . .). Yeast breads are pretty forgiving. Try with one "unit" (cake, packet, whatever) and see how it works. Very few people have ever inadvertently created a dough golem.
If you make your sourdough according to any of the methods you can find online, I've found that 200g of starter substituted for 100g of flour and 100g of water works well. Try it and see.