come across something means find unexpectedly (e.g. I came across these old photos when I was tidying the closet.)
come apart means separate (e.g. The top and bottom come apart if you pull hard enough.)
come back: (e.g. Tom is leaving tomorrow and coming back on Saturday.)
come down with something means become sick (e.g. My nephew came down with chicken pox this weekend.)
come forward means volunteer for to task or to give evidence (e.g. The woman came forward with her husband’s finger prints.)
come from place means originate in (e.g. The art of origami comes from Asia.)
come up means be introduced in a conversation (e.g. Some interesting matter came up in our discussion yesterday)
come up with an idea, a suggestion etc. means produce an idea (e.g. Ann is very creative. She’s always coming with new ideas)
count on somebody/ something means rely on (e.g. I am counting on you to make dinner while I am out.)
cross something out means draw a line through (e.g. Please cross out your old address and write your new one.)