An aspect is a way we look at something. With verb forms, there are three aspects:
simple, continuous and perfect.

The simple aspect emphasises that an action is complete.

The perfect aspect emphasises that an action is completed before another time.

The continuous aspect focuses on the action and duration (how long it lasts), rather than the result. It is used to show that an activity is temporary and its duration is limited.
In contrast to the continuous aspect, we usually use simple tenses to talk about facts, permanent situations, finished actions and habits. Some verbs - called state verbs - are not usually used in the continuous: verbs that describe personal feelings (to love, to prefer), the senses (to hear, to smell) and thoughts (to believe, to understand).

The Continuous aspect.  We use continuous aspect to talk about:
actions that we see happening over a period of time
What have you been doing since you graduated?

actions is progress when another thing happens
I was having a great time at the party when my dad arrived and dragged me home!

temporary or incomplete situation
I am living with my parents until I can find a house.

repeated actions (mostly annoying)
He is always playing her music loudly.

situation is in the process of changing
The economy is getting worse.

plans
I was thinking of going home this weekend.

tentative ideas (to avoid being too direct with a request)
I was wondering if you could lend me some money.

actions in progress at a particular time.
Everyone seems to be working at the moment.

The Perfect aspect
The perfect aspect looks back from one time to another and emphasises that an action is completed before another time. In some cases, the exact time may be unimportant or unknown. Sometimes the event is incomplete. It started in the past and still relevant now.

We use the present perfect to look back from now to a time before now.
I've lived in London since 1999.

We use the present perfect continuous to focus on the length of time the action takes.
I have been waiting for hours.

We use the past perfect to look back from a time in the past to a time before that.
I had to go back because I'd forgotten my passport.

We use the past perfect continuous to focus on the lengh of time the action takes.
I'd been doing the same job for fifteen years.

We use future perfect to look back from a time in the future to a time before that.
By next week we will have finished the project.

We use will have + past participle to make predictions about the present or the future.
Don't call the house, she'll have left for work by now.

We use future perfect continuous to focus on the length of time the action takes.
In 2020, I'll have been living here for 20 years.

We use the perfect infinitive after verbs like seem and appear to look back to a previous time period.
He seems to have forgotten his password.

The perfect aspect can be used with different time periods.
It's great to have finished my exams.
She said she was sorry to have missed your party.
We hope to have done the work by 5.00