Language is the words and phrases used in a piece of text.
Language Analysis is used to find out what types of words and phrases are used and why they are used.
Basically you look at the words/phrases used and label them as "repetition" or "this word has been used to create tension" etc.
Examples of Language Techniques you could label/analyse in a poem are:
•repetition
•metaphor
•personification
•sensory language (language that appeals to the senses)
•similie
•rhetorical question
•onomatopeia
•hyperbole (exaggeration)
my explanation is quite vague so here's a video that might help you:
https://youtu.be/bLKDSbEihmU
it's a uk gcse video but if you're not from the uk or not doing gcses it can still help with understanding language analysis, just skip to 8:15