What is the difference between “ɪ”, "i", “i:”? Is “ɪ” lax and short, "i" tense and short, "i:" tense and long?
You can hear what the IPA letters are supposed to sound like here. The terminological difference is that [i] is "close" and [ɪ] is "near-close", but non-IPA tradition tems that distinction "tense" and "lax", though sometimes it is treated as respectively [+ATR] and [–ATR]. The ordinary letter ":" is not official IPA, but it is widely used instead of official "ː" to indicate segmental length. But when applied to English, "i" is highly ambiguous, so you'd have to determine the interpretation from context.