1. Cohesion
Cohesion describes the way in which a text is tied together by linguistic devices, such as And so we see , Additonally , Therefore , However . . . and On the other hand . . .

2. coherence
A text has coherence if its constituent sentences follow on one from the other in an orderly fashion so that the reader can make sense of the entire text.

3. continued
Time flies like an arrow. On the other hand, fruit flies like a banana. Cohesive but incoherent? 
A little, but not entirely, like Colorless green ideas sleep furiously.

4. continued
Cohesion is "the glue that sticks a sentence to another in a paragraph or a paragraph to another in a text."
A text can be cohesive through the use of the following devices:
Repetition. In sentence B (the second of any two sentences), repeat a word from sentence A.
Synonymy. If direct repetition is too obvious, use a synonym of the word you

5. continued
Synonymy. If direct repetition is too obvious, use a synonym of the word you wish to repeat. This strategy is call 'elegant variation.'
Antonymy. Using the 'opposite' word, an antonym, can also create sentence cohesion, since in language antonyms actually share more elements of meaning than you might imagine.
Parallelism. Repeat a sentence structure. This technique is the oldest, most overlooked, but probably the most elegant method of creating cohesion.

6. continued
Transitions. Use a conjunction or conjunctive adverb to link sentences with particular logical relationships. There are many kinds of transitions.
Coherence means that the text is easy to read and understand because the text follows a certain kind of logical order and the organization of ideas is systematical and logical.
Some kinds of logical order:
chronological order, spatial order, order of importance