けれども is the more formal (full version) of the conjunction particle けど. Like けど, it usually carries the meaning of 'but', but because of its formality, sounds a bit more like 'although', or 'provided that'. It simply highlights that 'while thinking about (A), (B)'. Meaning that the (B) phrase is important, or needs to be considered.

• 私（わたし）は１０キロ走（はし）ったけれども、疲（つか）れていません。
  I ran 10km, but I am not tired.
• 温泉（おんせん）は熱（あつ）いけれども、気持（きも）ちいいです。
  Onsens are hot, but they feel good.
• あの人（ひと）は綺麗（きれい）だけれども、怖（こわ）いです。
  That person is beautiful, but scary.
• これはゲームだけれども、面白（おもしろ）くないです。
  This is a game, but it is not fun.

As can be seen from these examples, だ will be required when using this conjunction after a な-Adjective, or a noun.
As a reminder, please see below for a list of the most casual form of 'but', to the most formal.
Casual - けど - けども - けれど - けれども - が - Formal

• このパソコンは古（ふる）いけども、便利（べんり）だ。
  This computer is old, but useful.
• 薬（くすり）を飲（の）んだけれど、まだ頭（あたま）が痛（いた）い。
  I took medicine, but my head still hurts.
• 走（はし）るのは疲（つか）れるけれども、楽（たの）しいです。
  Running is tiring, but it is fun.
• 田舎（いなか）は静（しず）かだが、やる事（こと）が無（な）い。
  The countryside is quiet, but there is nothing to do.