切符とチケットと”券”

切符:            You can use 切符 as single word and especially used for Train Ticket, 電車の切符.

チケット:    Includes 切符 and 券. Ticket written in Katakana. You can use exactly same as ticket in English.

券:                Is always used with other words like (purpose) + 券.

                    e.g.入場券 (entering ticket), 乗車券 (boarding ticket),当日券 (Today's ticket), 航空券 (air ticket), etc.

                    I don't use 「券」 itself like 電車の券. In this case, I say 電車の乗車券.