I think your plant is a pokeweed, Phytolacca americana. I have lotsa lot in my yard in Massachusetts. It has been identified by friends. There are also questions on ourOur sister site, Gardening and Landscaping that discuss ithas a number of questions about pokeweed. I think this has the best pictures and identification.
To answer your question though, the simplest thing for me is to search using Googledo an internet search. (It probably works with other search engines, but I've only ever used Google.) Pick out some Choose words that characterize the plant, and see if it comes up. Even if you know only a little, it's possible to stumble on it.
In yourYour case, it turned out to be was relatively easy., especially if I'm correct! I don't have a description of the plant as a whole plant, andbut the most prominent feature I see in your picture isfeatures, including the stem and the berries, are clear. I went to Google and typed inGoogled "plant with long purple stems and purple berries." The first thing that came up was a list including some websites with descriptions and care information. That's often enough, depending on the plant and how much you want to learn about it. There are closely related plants, though, so you do need to be careful.
- (Many gardeners choose Wikipedia as their primary source of information source. It's in many languages, and has easily accessible scientific detailsa lot of links to other Wikipedia pages. It's not generally my favorite, though, as it's. It's harder to navigate and, doesn't always have the best pictures, especially on its home page, and their sources aren't always reliable.)
- The plants that most closely match your description generally appear first. As you'll see, the farther down you look farther down, thethere are more you start to see plants with the same general characteristics but don't look quite like your plant. If you want to go farther, click on one of the pictures that most closely matches your plantour pylant. A smaller group of pictures will come up, with links to websites. By using this method, I chose the very first picture and was led to the "Illinois Wildflowers" site, which opened the page clearly identifying it. http://www.illinoiswildflowers.info/weeds/plants/pokeweed.htm. (Again, search engines differ, so just pick one that most closely resembles your plant.)
To make sure you're getting the information is most accurate information, I recommend choosing a picture that is identified as coming from a gardening or plant identification website. Blogs often change, and may not be around if you want to find them later or get deleted. Other sites, like Pinterest, have good pictures but not necessarily much more than that. Some of those areAn example is Pinterest, which is member-based, and also change and disappear over timeever changing. Again, though, ifIf you just want to see more pictures of your plant though, that's a fine choice.