Early in the play we can learn about Hamlet's feelings as least as far as Ophelia understands them. In the conversation with her father he confronts her about her relationship with Hamlet, but Ophelia replies with assurance of Hamlet's feelings for her. Her first comment is "he hath, my lord, of late made many tenders of his affection to me." We don't know what those tenders are, but can assume nice words or perhaps even poems or gifts. She takes them to be sincere expressions of Hamlet's regard for her. Polonius makes them seem less than that. He suggests that Hamlet is not being true, but Ophelia again defends the relationship saying, "he hath importuned me with love in honorable fashion." Again, we don't know exactly what has been said but have not reason to think that Hamlet is insincere with Ophelia. She is vehement in defending Hamlet when she says that Hamlet "hath given countenance to his speech, my lord, with almost all the holy vows of heaven." Of course, Polonius doesn't trust any of this and calls Ophelia a young fool for love, but as an audience, we have no reason but to believe, as Ophelia does, the honest emotions he has seemed to share with Ophelia.
We don't learn of Hamlet's true feelings until the grave-side scene far later, and at the beginning his feelings for her appear to be quite conflicted.
We know that both Polonius and Laertes have counseled Ophelia to stay away from Hamlet, and she has agreed. What is more difficult to understand is how Hamlet feels about this separation, particularly since he does not know the reason for it.
We also know that Hamlet went to Ophelia after seeing his father, clearly suggesting that he had some desire to share with her this most momentous vision, of course she is confused and runs from him to her father, leaving him with further confusion perhaps about her feelings for him.