Enclosing a porch for living space is a major task, simplified if the existing porch floor and roof can be used without major change. Then enclosing the porch is framing walls, making any revisions to doors and windows in the existing house wall, adding exterior covering and finishing interior walls with insulation and drywall. It probably will require some help — and, if any plumbing or electrical work is involved, will require some professional assistance.
Plan your enclosed porch. Decide whether you need to add heating/cooling, electrical service or plumbing; those will require hiring professionals and should be planned first. Then determine whether you'll need to close any doors or windows in the main house and what sort of doors and windows you will need in the new living space. Decide how you will finish the exterior — match the existing house or use different material, perhaps wood siding on an existing brick structure. Make a list of materials and amounts and order them.
Remove old siding and other elements from the existing house as well as any railings or other impediments on the porch; you want to start with just a floor (preferably concrete) and a roof. If the roof columns are wood posts and are sound, they can be used; if they are metal, you may want to replace them (this will require making a temporary roof support while you pull out the old columns and install the new ones) or encase them in a wood frame.
Install a bottom plate for your new walls. Use double 2-by-4 treated boards, with an insulating moisture barrier underneath. You can drill into the concrete and cement in anchor bolts that go through the bottom plate or use special concrete nails or fasteners to secure the bottom 2-by-4; it must be solid. Then install a top plate; if the porch roof has a wood beam, you can use this. Then nail "king" studs (vertical frame lumber, usually at the left and right of a window or door opening, that runs continuously from the bottom plate to the top plate) at each end of the wall to the existing house wall or wooden corner posts.
Frame your wall with 2-by-4s, spaced 16 inches apart on center. Frame for any doors or windows; nail horizontal members at the top rough opening (and bottom for windows), then support with a vertical part stud. Nail "cripple" (short support) studs at top and bottom of these openings, between the opening and the roof or floor. Make sure all corners are square and plumb.
Sheath the outer wall with oriented strand board (OSB), weatherproofing wrap and foam-board insulation. Then install any windows or doors; put flashing and caulk around openings to seal them. Finish the outside with whatever cladding you have chosen — wood (or artificial wood) planks, special wood siding, cedar shakes.
Staple fiberglass insulation between the studs; some manufacturers now recommend also taping seams and connections with other materials. Then install drywall with drywall screws and tape the joints; you can use plastic tape with an adhesive backing or paper tape, which you install with joint compound. Cover all screws and other blemishes with compound, then sand the wall smooth for paint.