Wow. I'll be honest that 90% of those words mean absolutely nothing to me and that I'm about to start Googling them. Thank you so much!
If you don't mind some hand holding, it sounds like this is something I can confidently do. I'll even let you make fun of me when I ask occasional stupid questions.
Don’t be at all intimidated- most people that are highly mechanically inclined like you make good carpenters- wood is just another medium.
Quick primer-
D Log- those are the fake logs- they are made from pressure treated pine and overlap each other with a notch along the bottom edge . The stain /sealer and horizontal design prevents water penetration and allows run off, so they tend to perform well. On that structure those may be the most durable of all the exterior wood on it.
The door opening is a big hole filled with untreated wood sitting in untreated wood basically.
OSB - that is the chip board you see painted and exposed under the porch. It is designed to be shielded from moisture for long term performance. Osb stands for oriented strand board. When it’s used on the horizontal it is called decking and usually thicker to carry weight.
The Jambs of a door or window are the side legs of the frame.
The door itself is called the slab or blank.
The horizontal pieces of a door are rails, the vertical pieces are stiles.
The sill is the bottom part, and it and the threshold are often considered the same component.
Sheathing - this is just the term for what clads the framing of a roof or wall- your walls are likely 2x 4 or 2x6 and the sheathing is the OSB we see exposed under the porch and is likely behind all the logs.
The Band is the perimeter framing of the floor, normally a 2x10 sitting on a treated 2x8 laid flat called the plate.
The joists are the floor framing members (2x10 typically) that run side by side to the band and the decking is usually 3/4 osb or plywood attached to that. Their determined size is correlated to their length and spacing in span tables)
Ice and water shield is sold in many names, it is a roll product and widely used in your region for roof work especially. It is basically a flashing that seals the fasteners used to attach it.
Flashing is any sheet or roll or similar product designed to shield the structure from water- it has to always be installed so it cant hold water behind it , or it will accelerate damage.
Zip tape flex is just a highly bendable tape made for the corners of openings in zip sheathing- a green , coated OSB sheathing that is the big noise right now- and will ultimately create millions of dollars of damage because field carpenters will mistakenly think it makes the structure immune to bad practices. Thinking something is bulletproof is worse than knowing it isn’t when it comes to mass use.
The corners of door openings and windows are where most failures occur. We flash the sill, then the corner over that and then the jamb over that.
Think of all the wood as a skin only.
On your job getting the door opening flashed well all the way down to the masonry and lowering the porch and spacing it out are the 3 critical steps, the rest is just repair and cosmetics. The porch surface decking can even stand off the house 1/4” - 1/2 “ and water can then fall straight down. Nature abhors a vacuum.
In your case the D logs are likely serving as a shield quiet successfully- with the openings being the weak point. Even if no tar paper is behind them or they are tight to the structure. Keeping it clean at all penetrations and openings and sealing gaps at windows may be very good long term- just try to keep water out from behind it any way you can. Its a tough product.