What am I supposed to do?

Now, I'm not a good player but I'm not a bad player so try to keep that in mind here. When I'm laning and I die once or twice so I decide to play safe and hide under my tower but there champ easily dives under tower and kills me, what am I supposed to do?

Example: I had a game where I played Vayne against a Cait and Malph bot. I was doing ok, held my own until malph hit lv 6. He ulted me and combo wombo'ed me. He did about 400 damage to me and cait finished me off with an ult. Fine, ok. I return to lane and hide under my turret. I can't raelly get any farm but I figure at least I'm not feeding. Then malph ults me under my tower doing about 400-500 damage to me and Cait q's and ults me I die. I go back to lane, and same thing happens. What is it I'm supposed to do at this point? I'm still only level 8 ish, can't get any farm without dying.