(someone) just (did something)

One of the uses of "just" is to express that something happened very recently. It can mean a few minutes before:

I'm sorry, he just walked out to go get lunch.

Or immediately before:

What did he just say?

Or it can mean a few years:

Mankind has just started to study ways to understand and control DNA.

But in any case, "just" means a short time before.

You're welcome to (do something)

This is a way to offer something to someone:

You're welcome to use my car if you need to go anywhere.

You're welcome to come with us if you want to.

Offering things in this way is friendly and low-pressure. In other words, it doesn't make the listener feel like they have to accept the offer.

Strangely enough, (sentence)

Use this phrase when something surprising or coincidental happens. For example, if a friend tells you that she recently got a new job, and you also got a new job recently, you can respond:

Strangely enough, I just started a new job last week!

Another example: someone asks you whether you've spoken to your brother lately. Usually you speak with him every week, but the last time you spoke to him was 3 weeks ago. You can say:

Strangely enough, no. I haven't heard from him for a few weeks.

a bike

"Bike" is short for "bicycle":

I never learned how to ride a bike until I was in my teens.

Sometimes people also call motorcycles "bikes":

Where did you park your bike?

Usually you can guess based on the situation whether someone is talking about a bicycle or a motorcycle.