You can use Office for free for one month by downloading the Office 365 trial. This includes the Office 2016 versions of Word, Excel, PowerPoint, Outlook, and other Office programs. Office 365 is the only version of Office with a free trial available. Signing up for the free trial will require a valid credit card, but you will not be charged until the start of the second month. Canceling before the end of the first month will prevent any charges and allow you to use the trial for the entire first month. You can download the trial from the official Office website. Visit products.office.com/try to open the trial page. This will begin the sign-up process. You'll be prompted to log in with your Microsoft account. You can use any Hotmail, Live.com, or Outlook.com email address to sign in, or you can create a new account for free. Creating an account is required for the trial. You'll need to enter a credit or debit card in order to start your trial. This card will not be charged immediately, but you will be charged the monthly Office 365 fee if you don't cancel by the end of the trial. After creating your account and entering your credit card information, you'll be given a link to download the Office 365 installer. The installer itself is very small, and should only take a few moments to download. Once the installer has downloaded, run it to begin the actual download and installation of Office. You may be prompted to enter your Microsoft account again before the download begins.  During installation, you'll be given the option to select which Office products you want to install. You can save time and hard drive space by deselecting the programs you won't be using. You can always install them again later if you end up needing them. The installation process will take a fair amount of time, especially if you have a slow internet connection. You'll be able to find your newly-installed Office programs in your Start menu. You can use all of the features of the programs for your entire trial.

TL;DR in Chinese:
免费试用Office 365一个月。 浏览Office试用网站。 点击“免费试用1个月”，开始进行注册。 用你的Microsoft帐户登录，或是创建一个新帐户。 输入有效的信用卡信息。 下载Office 365安装程序。 运行安装程序。 启动Office程序。