Translation:If I miss my train, I will take the bus.
"Ob" is used in an interrogative clause (used for indirect questions and such), i.e. "Sie hat mich gefragt, ob ich Katzen mag"— "She asked me if I like cats". "Falls" is used in a conditional clause, i.e. "Falls ich das nicht überlebe... Lösch meinen Browserverlauf."— "If I don't survive this... Delete my browser history."
"Will" is implicit. Commonly, particularly in conversational German, the future tense is implied.
"However, German usually relies on the present tense to indicate the future (implied future) and uses time expressions, such as tonight, tomorrow, etc. so the actual future tense is not quite as common in German as it is in English. "