The Act of Surrender

When the police shouts " Hands up "
The thief listens to the police

So the Act of Surrender to Lord Krishna is to listen , to follow the instruction of Lord Krishna

so here is the greatest instruction of Lord Krishna in Bhagavad gita

man-manā bhava mad-bhakto

mad-yājī māḿ namaskuru

mām evaiṣyasi satyaḿ te

pratijāne priyo 'si me

TRANSLATION

Always think of Me, become My devotee, worship Me and offer your homage unto Me. Thus you will come to Me without fail. I promise you this because you are My very dear friend.

http://vedabase.net/bg/18/65/en

http://vedabase.net/bg/18/66/en

The process of surrender to Kṛṣṇa is described in the Hari-bhakti-vilāsa (11.676):

ānukūlyasya sańkalpaḥ

prātikūlyasya varjanam

rakṣiṣyatīti viśvāso

goptṛtve varanaḿ tathā

ātma-nikṣepa-kārpaṇye

ṣaḍ-vidhā śaraṇāgatiḥ

According to the devotional process, one should simply accept such religious principles that will lead ultimately to the devotional service of the Lord. One may perform a particular occupational duty according to his position in the social order, but if by executing his duty one does not come to the point of Kṛṣṇa consciousness, all his activities are in vain. Anything that does not lead to the perfectional stage of Kṛṣṇa consciousness should be avoided. One should be confident that in all circumstances Kṛṣṇa will protect him from all difficulties. There is no need of thinking how one should keep the body and soul together. Kṛṣṇa will see to that. One should always think himself helpless and should consider Kṛṣṇa the only basis for his progress in life. As soon as one seriously engages himself in devotional service to the Lord in full Kṛṣṇa consciousness, at once he becomes freed from all contamination of material nature. There are different processes of religion and purificatory processes by cultivation of knowledge, meditation in the mystic yoga system, etc., but one who surrenders unto Kṛṣṇa does not have to execute so many methods. That simple surrender unto Kṛṣṇa will save him from unnecessarily wasting time. One can thus make all progress at once and be freed from all sinful reactions.

A tapasavi is one who rejects all that unfavourable for devotional service & accepts all that is Favourable for devotional service

Taking shelter means that we have to be convinced that we are stuck in MAYA (illusion), we have so many bad habits, we are attracted to dead flesh and bones, hence the only way that we can be saved by falling into illusion is by CRYING out to Krishna to help. This is basically taking shelter. TAKING SHELTER of someone means you know that there is really no other hope. So as long as we are not convinced about this fact (in our heart), we cannot truly take shelter of the Holy Name.

One would take shelter when he knows that he does not know anything.

he understands that nothing is in his control & everything is in Krishnas control

when we realise that how much we donot know we take shelter ....... HH Radhanath Swami Maharaj

So in surrendering to Krishna one has to take shelter of the divine nature of Krishna ie Radharani simply because as devotional service is the ultimate thing to liberate from body then

what service will please Krishna ? do we know this ?? absolutely NOT

but Radharani is the only person who knows what pleases Krishna so we have to shelter of Radharani to learn & co-operate in pleasing Krishna .

This is basically Surrendering .