Operations can be reverted by pressing Undo/Redo / buttons on General toolbar.

Paste names, InChi, CAS numbers directly onto the canvas, they will be converted into chemical structures right away.

The easy way to modify or add new properties to an atom/bond/selection to right click on it and use an option from the pop up menu.

You can introduce any kind of element and a lot of query features from Periodic Table dialog. Try out the Advanced panel as well.

Use build-in structure templates, choosing Insert>Template Library from menu.

Import peptide, DNA, RNA sequences from menu Edit>Source.

Simple paste IUPAC name from Structure>Structure to name menu; you can add IUPAC numbering as well (menu View>Advanced>Atom numbering>IUPAC numbering)

Calculate chemical properties like pKA, logD, Solubility using the options of Calculation menu (additional license needed).

Is your molecule chemically correct? Check it pushing Check Structure button from General toolbar.

Press Ctrl+2 (or Ctrl+3) if you want to clean your molecule in 2D (or 3D ).

Check your molecule in online databases (Chemicalize, Chemspider, Pubchem) from File menu of MarvinSketch.