Realise is the British English spelling of the verb meaning:
1. To become fully aware of something as a fact; understand clearly
2. To achieve something desired or anticipated
3. To convert an asset into cash
4. To bring into concrete existence
In American English, the spelling is realize.
Realise 这词儿在英式英语里可太常见了，咱给您掰开了揉碎了讲讲：
1. 明白过味儿来，整明白了（比如：I suddenly realised I left my keys at home 突然发现钥匙落家了）
2. 把事儿给办成了（比如：She finally realised her dream of becoming a doctor 她终于圆了当医生的梦）
3. 把东西变现（比如：We need to realise some assets to cover the debt 得变卖点家当还债）
4. 把想法给整成真的（比如：The architect realised his vision in this building 设计师把这栋楼给整出来了）
美式英语里这词儿拼写成 realize，意思都一样，就是写法不一样，您可别整混了！
小贴士：这词儿在口语里用得可勤了，特别是第一个意思，老外整天"I realise now..."这么说话，跟咱北京人爱说"我琢磨明白了"一个意思。