First, the meaning of expression is different
1, because it started at a certain time. For example, from two years ago, that is to say, two years ago can be regarded as the starting point of time.
2. It means going from one time to another. For example, two years is interpreted as two years, which means that a period of two years can be regarded as a period of time.
Second, the usage is different.
1, followed by a little time, specific time, "since, since" is used to explain the start time of the action, and is used to start the event, action or state.
2, for followed by a period of time, the predicate verb in the sentence should also be a progressive verb.
Third, the tense is different
When the words 1 and since refer to a specific time, the verbs used in the main sentence are either the present or past perfect tense or the present or past perfect continuous tense. Because it cannot be used in the future tense.
The word 2.for can be used in all tenses.