understand
v.v. to know the meaning of what someone says or how something works. You use this when you get the idea or follow an explanation.
v. to perceive the intended meaning of words, a language, or a person; to grasp the significance, implications, or importance of something. Stative in most contexts, though it can appear in progressive forms in informal register to indicate a developing state of comprehension.
I do not understand this math problem.
She speaks very quickly, so it is sometimes difficult for new students to understand her instructions.
While the basic mechanics of the software are easy to understand, mastering the advanced features requires a deep knowledge of the underlying code.
From Middle English understanden, from Old English understandan (“to understand”), from Proto-West Germanic understandan (“to stand between, understand”), from Proto-Germanic understandaną (“to stand between, understand”), equivalent to Old English under- (“between, inter-”) + standan (“to stand”) (Modern English under- + stand). Cognate with Old Frisian understonda (“to understand, experience, learn”), Old High German understantan (“to understand”), Middle Danish understande (“to understand”). Compare also Saterland Frisian understunda, unnerstounde (“to dare, survey, measure”), Dutch onderstaan (“to undertake, presume”), German unterstehen (“to be subordinate”).
The verb is usually stative and not used in the continuous (-ing) form, though 'I am understanding' is occasionally used to mean 'I am starting to see'.
I am understanding youI understand youAs a stative verb, it is generally used in the simple present rather than the present continuous.