The sharing function in the Math Learning Center apps allow you to send to your students the specific virtual manipulatives that you have designed in the apps. For example, when using the fractions app you can design a virtual manipulative for students to practice identifying and writing fractions. You can then share your virtual manipulative with your students by giving them a direct link to it or by having them use an activity code that is automatically generated for you. In either case, your students don't need to sign into any kind of account to access the virtual manipulative that you share with them.
With the exception of the flashcards app, all of the Math Learning Center's free apps are designed to provide you and your students with virtual manipulatives. Geoboard is a good example of how all of the apps are intended to be used. Geoboard is a free app on which students stretch virtual rubber bands over pegboards to create lines and shapes to learn about perimeter, area, and angles. Another app features US currency to help students learn to add and subtract money. The Pattern Shapes app is designed to help students recognize and develop patterns by moving colorful shapes into place.
It is important to note that except for the flashcard app all of the Math Learning Center apps are virtual manipulatives designed to be used as a part of lesson plan not as stand-alone practice apps. You will need to provide your students with feedback when they are using these apps. The new sharing option makes it easier for you to share with your students and for your students to share their work with you. They can provide a link to their work for you to see what they've done.