Student or Learner
When I read I'd, how do I know when It means "I had" and when It means "I would" ?
And I don't know exactly when to use Id ( meaning I had) and when to use I've.
For example, can I say: "I'd drop you a line to let you know"? Or should it be "I've dropped you a line to let you know"?
Welcome to the forum, Pablo.
1. The context reveals the meaning. "I'd been lost for an hour before somebody found me" can only mean "I had been lost ..." and "I'd cry if my hamster died" can only mean "I would cry ...'
2. "I'd" ("I had") is the past perfect tense and "I've" ("I have") is the present perfect tense.
3. "I'd drop you a line to let you know" can only mean "I would drop you a line ..." but needs something else to follow, such as "...but I haven't got time".
"I've dropped you a line ..." is fine.
You must not put an apostrophe in "Thanks".