There are multiple ways you can get into Ukraine
There is every day train from Warszawa to Kiev, however find ticket can be difficult.
The fastest way to get to Lviv or Kiev is take a train from Warszawa or Krakow to city Przemyśl, which only 10 km from Border Cheakpoint Shehyni or if you outside of Poland you can tacke a flight from London to closest airport Rzeszów-Jasionka (95 km from Przemyśl)
From Przemsl is every day train to Kiev and Lviv (Lviv - Przemsl only 3 hourse ride by traine)
Border Cheakpoints: Porubnoe(the closesst city: Chernivtsi UA), Solotvino, Diakovo(the closest city Uzhhorod UA)
The best way to travel by plane to city Suceave that 45 km away from border cheakpoint Porubnoe.
London Luton - Suceava
Milano Bergamo - Suceava
Dortmund - Suceava
Munich West/Memmingen - Suceava
Rome - Suceava
From Chernivtsy (35 km from Porubnoe), can be taken train to Kiev or Lviv, that departure everyday at evening.
Border Cheakpoints: Mamalyga(to city Chernivtsi 60 km), Kelmenci, Rossoshany, Sokiriani
Closesst Airport in Chisinau
There are flits from Vienna, Brusselss, Prague, Larnaca, Paris, Munich, Hamburg, Milano, Rome, Venice, Barcelona, London, Liverpool
From Chisinau to Border Cheakpoint Mamalyga is 250 km the best way to get to Ukraine is bus that depurture from Chisinau and arrive in Chernivtsi city in Ukraine
Buses Mamalyga - Chernivtsi: prices and schedule, buy coach tickets online