Not every gap is a problem. Not every hole should be sealed.
Your home breathes, and some of those breaths are on purpose
Stand near a window on a cold, windy day and you can feel the draft. Stand near an exterior door with worn weatherstripping and you can see daylight at the edges. These are real energy losses, and sealing them is one of the most cost-effective improvements a household can make. But not every opening in a building envelope is a defect. Some of them are there because the building needs them.
Weep holes in brick let trapped moisture drain. Soffit vents keep attic air circulating so moisture does not condense on the roof deck. The gap around a gas appliance vent exists because combustion needs air. A dryer exhaust duct leads outside on purpose. Seal any of these and you create a problem worse than the one you were trying to solve: trapped moisture, mold, poor combustion, or a fire hazard.
Two materials, two jobs
The distinction is simple once you see it. Caulk seals stationary gaps between components that do not move relative to each other: where trim meets a wall, where a window frame meets siding, where a pipe penetrates a surface. Weatherstripping seals movable joints where one component opens and closes against another: doors, operable windows, attic hatches.
Using the wrong one in the wrong place does not work for long. Caulk on a moving joint cracks. Weatherstripping on a stationary gap peels. The reading covers both in detail, including what product types suit what conditions.
The hardest part of sealing a home is not applying the caulk. It is deciding which gaps are meant to stay open.
Your walkthrough
The action step asks you to walk the exterior of your home, or your unit's windows and doors if you are in an apartment. You are looking for three things: failed caulk lines that have cracked or pulled away, worn weatherstripping that no longer makes contact, and gaps where air or water is getting through. For each one, note whether it is a gap that should be sealed or one that might exist for a reason. That list becomes part of your Maintenance Map, and the gaps you can confidently identify as problems are your starting projects for the skills the readings teach.
The reading for this module
Read as many as you need. The first gives the overview; the second goes deep on air sealing and insulation.
Find the gaps in your building envelope.
Walk the exterior of your home or your unit's windows and doors. List every failed caulk line, cracked weatherstripping, or gap where air or water is getting through. For each, note whether it should be sealed or might be a designed opening. Record what product type would fit.