If you're using a traditional rocket (i.e. anything that accelerates forwards by expelling something from the ship backwards), then the rocket equation applies:
$$M_0 = M_1 \exp(\Delta v/v_e)$$
$M_0$ is your rocket's "wet mass", i.e. the mass of the rocket plus the propellant at the beginning of the journey
$M_1$ is the "dry mass", the mass of the rocket at the end of the journey
$v_e$ is the exhaust velocity, the speed that the propellant is expelled from the rocket
$\Delta v$ is the delta-v of the journey; in relativistic contexts this is the integral of proper acceleration times proper time (acceleration times time as experienced by the rocket)
And $\exp$ is the natural exponential function (e to the power of x).
One way to get a 10 year journey to Proxima (4.25 light-years away) is to accelerate at 1g for 0.42 years proper time (0.43 years back on Earth), coast for 9.15 years proper time (10.02 Earth years), and then decelerate for another 0.42 years proper time to arrive at the destination. (Max velocity is 40.6% of the speed of light; total time experienced by crew 9.99 years, total time according to Earth observer is 10.88 years.) You can spin for gravity during the coasting phase, just design your habitat module to be able to handle gravity from both the thrust direction and the radial direction.
With a fusion engine, exhaust velocities are around 10% of light speed IIRC, and the rocket equation tells you that you need... 234
about 5480 kg of propellant for every 1 kg of rocket and payload at the end of the journey. There's no possible way to carry such an insane amount of propellant. So you'll need to invoke some fictional engine technology.
With a photon rocket that can directly convert mass-energy of your fuel to an enormous planet-scorching laser (do not point your exhaust within an AU of anyone or anything you love), you would need about 1.37 kg of mass-energy convertible fuel per kg of rocket. Much more manageable. 574