The primary function of a physical therapist is to evaluate and treat people who have "functional limitations" that affect their daily living. This could be due to pain, weakness, lack of flexibility, decreased balance, etc. A physical therapist evaluates the neuromuscular skeletal system to look for reasons why these things may be happening and provides a "physical therapy diagnosis" and recommends and implements treatments.
These treatments may include "gait training" (showing someone how to walk, etc), balance training, manual techniques, exercises, education, stretching, massage and/or modalities.
One does not necessarily have to be "strong," but as a general rule, a PT should be able to lift 25# at least occasionally and be able to stand for long periods of time. Educational requirements in the US require a master's or doctorate level degree. Most programs are designed to be completed in 6-7, but it depends on how long it takes one to complete the prerequisite courses and your bachelor's degree.
The prerequisite courses usually involves a lot of science, math and psychology. Once you are in the program you must take gross human anatomy (human dissection) and all your physical therapy based courses including evaluation techniques, musculoskeletal coures, neurology, etc.
Blood is encountered occasionally in PT and will be more likely if you work in a hospital inpatient setting...you can be exposed to a variety of bodily fluids in this settings. Some settings also have PTs complete wound care which could include packing and debriding wounds. Other than that, it's generally a pretty clean job...especially in the outpatient setting.
The APTA has a great section for prospective students. Go to the educational programs section at http://www.apta.org