what is together.math?
Editor
together.math is an editor for math homework. It helps students show their work. It doesn't do it for them. The result is that you get something beautifully formatted to grade, and your students could focus on their math, not on how to write symbols.
Assistance
together.math has optional immediate correctness feedback. It evaluates whether a line of math was consistent with stated assumptions (those lines marked with (*)). It marks in red if they do not check out. You can see on the title page of the report whether the student used immediate feedback.
together.math also lets students manipulate algebraic equations with draganddrop. Again, the cover page of the report you have shows whether they used this feature (useful to know as it is fairly impossible to make outright mathematical mistakes with draganddrop).
Collaboration
together.math allows students to share the document with others, and collaborate with them live. Think "Google docs for math". The front page of your report shows whether your student worked with others, and how many minutes each person contributed.
QR code
You might have received a printed report, and you are wondering how authentic it is, as many students have the technical knowhow to change such a document. The QRcode, and the accompanying URL, will lead you to a version of the submission that was frozen upon submission. In the future, we will also integrate grading tools for you here.
tips and tricks

Help
To use drag and drop, don't edit a field. If you are in editing mode, click escape to exit it before using drag and drop.
When you edit a text field, the menubar appear below. Hover over buttons to see tooltips.
Click the "?" (Help) button on top bar to toggle the keyboard help screen for your system.

Syntax

Most algebraic terms are written as you might think. Use parentheses to make clear what you want grouped, if the need arises.

abs() is written with vertical pipes left and right of the term: x.

ceil(), floor() and round() will do rounding.

nroot(x, n) is the nth root of x.

sqrt(x) is the squareroot of x.

"approx" will fit into the window where the equal sign normally is.

Assumptions are created by marking them in the comment field with (*) or (*1) etc. One asterisk for a sectionwide assumption, two (**) for a global assumption.

Numbered equations can be used to rightclick substitute a variable.

If you create a quadratic normal form for a variable, rightclick can insert the quadratic formula for you.

Differentials are written as "d.x" for dx, "d.y" etc.

Integrals follow LaTEX conventions: "int", then "_" and the lower bound, then "^" and the upper, then the term, ending in a differential.

Derivatives start with the operator "d./d.x" and then the term, or "d.(term)/d.x" as a complete fraction.

Missing things
together.math is not complete:

You cannot declare functions, or reason about unknown ones with calculus.

Systems with complex solutions might show interesting behavior.

Drag and drop needs many more drop targets  today, you cannot use it to solve things involving gathering or distributing terms.

You can only link to external images, not embed them.

The drawing control is ... special.