You should really learn to manage your money better.
你真的需要好好地理财了。
Somebody manages his/her money well.
某人很会理财。
Somebody can't handle/manage money.
Somebody is bad with money.
某人不会花钱，不懂理财。

Somebody is a penny pincher.
某人一毛不拔。
Somebody is stingy / cheap / tight / close-fisted.
某人很小气。
fist 本意为拳头，close-fisted 形容把钱抓在手里，握紧拳头不撒手。

You should always save for a rainy day.
要存点钱，以备不时之需。
save for a rainy day
存钱以备不时之需，未雨绸缪
Older generations in America tend to be more frugal than younger ones.
老一辈的美国人会比年轻人要节省一些。
frugal 节省的，节俭的

Somebody is in debt. 某人欠钱，负债了。
若要表示程度之深，可以讲成 be deep in debt. 比如：
Her husband Peter is dying of cancer and the couple are deep in debt.
她的丈夫 Peter 患了癌症，夫妻两人欠了大笔债。

control (all the) finances: 掌管经济大权
A husband controlling finances can lead to relationship trouble.
一个家庭如果丈夫管钱的话，夫妻关系可能就会出现麻烦和问题。

squander one's money 乱花钱，浪费钱
In less than three years he had squandered the entire family fortune.
在不到三年的时间内，他挥霍完了所有的家产。

splurge on something 花大价钱买某物（通常说话者认为不值得花那么多钱）
splurge on a new dress
花大价钱买了一条新裙子
You should let yourself splurge once in a while.
你应该允许自己时不时地挥霍一次。