And even if we do, will we colonize? Start up the next Galactic Empire?
Like all other animals we are closely attuned to our environment, more so than many of us actually realize anymore. In these days of electricity we can heat or cool our homes, spend half the night watching TV, or reading books, source food from all over the world so nothing is ever out of season, cross distances that took years in days. Yet we cannot escape the factors which shaped us.
I think there are five vital factors we will not easily overcome.
Our perception of timeI use the word 'perception' advisedly, because time is something we measure for ourselves to put ourselves into context, if you will. But whether we think the sun is rising where we are, or setting, our bodies are built to expect a 'day' of twenty-four hours or so, because that's how long it takes for our planet to revolve on its axis. What's more, if we are suddenly wrenched from one time of day to another, as happens with long distance air travel, it takes time for our bodies to adjust. (It's called jet lag) We don't know how long the 'day' is on those alien planets. They may be tidally locked, like the moon, or like Venus where the day is 116 Earth days long. Or they may whizz around their axis in hours like Jupiter, which rotates in a little under ten of our hours.
GravityWe have evolved to suit the amount of force the planet exerts upon is. The advent of space travel and weightlessness has proved how important gravity is to our ability to function. Without gravity our bones lose density and muscles atrophy. For our seven newly-discovered planets this is a huge plus.
AtmosphereMost of our atmosphere, what we breathe, is nitrogen, with twenty-three percent oxygen and a bunch of other gases in smaller quantities, including carbon dioxide. It also has a level of density. There's more of it at lower altitude (see gravity). See what happens to mountain climbers if they climb before becoming acclimatized. Their bodies can't cope. And if that mixture of gases changes past a certain level of tolerance, then what? We don't know anything about the atmosphere of our seven planets. As Donna pointed out, being in the star's Goldilocks zone doesn't prove much. Mars and Venus are both in our sun's Goldilocks zone, but Venus, which is about the same size as Earth, has a hellish atmosphere, and Mars, which is much smaller than Earth, has hardly any atmosphere at all.
TemperatureHumans exist in an apparently wide range of climates, providing they can find protection from the elements. But the range is actually not that wide in the scheme of things. That very dim star is therefore something of a worry if we actually want to roam around without spacesuits, and grow food.
LightEarth orbits a G class star which emits light towards the red end of the spectrum. We're used to seeing colors in that light. If we lived on a world orbiting a cooler star with redder light, or a brighter star with more bluish light, we'd see colors differently. But this is one where I think we'd get used to it very quickly.
Can it be done?The recent movie The Martian did an amazing job of illustrating the problems associated with trying to live on a planet with a dim sun, not much atmosphere, and cold temperatures.
Humans are adaptable. That's why the species has been so successful. But even so, we've only ever had to adapt to the extremes of one planet. If humans are to venture to other planets and live without space suits I believe we will have two choices; terraform the planet into another Earth or modify the settlers to cope with the conditions. That would mean physically very different races of humanity occupying different planets.
SF can offer plenty of examples. One that springs to mind is Moon and McCaffrey's joint effort, Sassinak, where members of the Star Fleet have different body characteristics, depending on which planet they come from. That can be accomplished through genetic engineering, or by creating cyborgs.
I admit I don't take that route in my own writing. I simply assume all planets are earthlike, with only small variations in light, heat, time and gravity. Moon and McDevitt both used terra-formed planets in their imaginary universes - although it's hard to terra-form planetary rotation, length of year, and mass. But that doesn't mean all those variations can't be found in the space surrounding the planets they dream up. It is the reality of space.
This is a very exciting time to be alive. As our equipment improves we'll be able to learn more and more about the planets out there. The James Webb telescope will be up and running soon, opening up more and more possibilities. The planet circling Proxima B is close enough for better study. I look forward to the results.