从今天开始，我要学习英语：From this day，I have to study English.
From this day:自今日起,从今而后；从今天；从今开始。
例句：From this day， you must be a stranger to one of your parents. 从今天开始,你将与双亲之一成为陌生人.
要：have to
例句：Sometimes things have to fall apart to make way for better things. 有时候要到达谷底，才会慢慢变好。
学习：study
例句：He entered Otago University to study arts and divinity. 他进入奥特哥大学学习艺术和神学。
从今天开始，我要学习英语：From today on, I need to learn English.
from today on:从今天开始；从今天起；从今天；从今日起。
例句:From today on, let's start to love ourselves, unconditionally! 从今天开始, 让我们去全心全意地爱自己.
要：need to
例句：Do not wait for good things to happen to you. You need to walk towards happiness. 不要等待好事降临，你要向幸福进发。
学习：learn
例句：He's still learning and when he hits his stride, he'll be unstoppable. 他仍旧处在学习阶段，一旦驾轻就熟后将势不可挡。
从今天开始，我要学习英语：I will study English starting today.
starting today:从今天起；今天开始；从今天；都从今天开始。
例句：We must act as soon as possible, starting today. 我们必须尽快行动, 从今天开始.
要：will
例句： I will return, find you, love you, marry you and live without shame. 我会回去，找到你，爱你，娶你，活的光明正大。《赎罪》
这句话是典型的中文常见表达，副词短语置于主谓宾结构之前，翻译为应英文时应该倒置，成为英文的正常语序。“从今天开始”，其实指的是“from now on”，即从现在开始。而动词“学习”其实意味的“努力学好”（learn well），或者“提高”（improve）的含义。
建议的译法：
I've decided to learn English well from now on.
I will improve my English from now on.