Yes, in many cases you can absolutely install an outdoor bench yourself with basic tools, and you do not need to be a seasoned carpenter to do it. If you are working with a freestanding bench, a simple wooden or metal bench kit, or a standard park-style bench on level ground, the job is very DIY-friendly. A drill, a level, a wrench, a shovel, some gravel or paver base, and a bit of patience will get you a long way. The key steps are to choose a flat or gently sloped spot, clear the area, set a stable base, and anchor the bench securely so it does not wobble or shift. For most patio benches and garden benches, you can handle this in an afternoon.
That said, there are times when hiring a pro makes more sense. If the bench is extremely heavy, made of stone or cast iron, or needs to be installed on a steep slope, retaining wall, concrete slab, or uneven ground, a professional can save you from injury and costly mistakes. You should also call a contractor if the project involves pouring a concrete pad, running electrical lines for lighting, or building a custom built-in bench attached to a house or hardscape. A pro will know how to handle drainage, frost heave, permits, and structural anchoring properly.
If you are still unsure, use this simple rule: if the bench arrives as a kit or a complete unit, the ground is level, and the tools on the packaging look familiar, go the DIY route. If you are changing the landscape, dealing with heavy materials, or modifying your home, get at least one quote from a professional. Either way, take your time with the base and anchoring. A well-installed bench should feel solid, sit level, and stay put season after season.