How MAVEN will import someone else's project into its own eclipse and use

There are no jar packages in the items copied from others, so how do you use them?

It is divided into two steps: 1. Import Package: file-->import-->maven-->existing Maven projects,ok!! Successfully imported, but another new problem came, no jar package, what to do?

2. Select the project, right-click-->maven-->updateprojects to get it done!

But somehow, the files are right, but the project Error!!! Don't worry!

3. Select item-Right-properties--> Select the third deployment Assembly, then add Maven dependecies to it

How MAVEN will import someone else's project into its own eclipse and use